Electrochromic rearview mirror incorporating a third surface metal reflector and a display/signal light

ABSTRACT

An electrochromic mirror is disclosed for use in a vehicle rearview mirror assembly having a light source positioned behind the electrochromic mirror for selectively projecting light through the mirror. The electrochromic mirror includes front and rear spaced elements each having front and rear surfaces and being sealably bonded together in a spaced-apart relationship to define a chamber, a layer of transparent conductive material disposed on the rear surface of the front element, at least one solution-phase electrochromic material contained within the chamber, and a second electrode overlying the front surface of the rear element in contact with the electrochromic material. The second electrode includes a layer of highly reflective material and a coating of electrically conductive material that is at least partially transmissive and is disposed over substantially all of the front surface of the rear element. The second electrode further includes a region in front of the light source that is at least partially transmissive. The electrically conductive coating may include a single transparent layer or a plurality of partially reflective and transmissive layers, or an electrically conductive dichroic coating. The light source may be an information display, such as a compass/temperature display as used in an inside rearview mirror, or may be a signal light as used in an outside rearview mirror.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 09/114,386, filed on Jul. 13, 1998, entitled "ELECTROCHROMIC REARVIEW MIRROR INCORPORATING A THIRD SURFACE METAL REFLECTOR," by Jeffrey A. Forgette et al., which is a continuation of U.S. patent application Ser. No. 08/832,587, filed on Apr. 2, 1997, entitled "ELECTROCHROMIC REARVIEW MIRROR INCORPORATING A THIRD SURFACE METAL REFLECTOR," by Jeffrey A. Forgette et al., now U.S. Pat. No. 5,818,625, the entire disclosures of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to electrochromic rearview mirrors for motor vehicles and, more particularly, to improved electrochromic rearview mirrors incorporating a third surface reflector/electrode in contact with at least one solution-phase electrochromic material. Heretofore, various rearview mirrors for motor vehicles have been proposed which change from the full reflectance mode (day) to the partial reflectance mode(s) (night) for glare-protection purposes from light emanating from the headlights of vehicles approaching from the rear. Among such devices are those wherein the transmittance is varied by thermochromic, photochromic, or electro-optic means (e.g., liquid crystal, dipolar suspension, electrophoretic, electrochromic, etc.) and where the variable transmittance characteristic affects electromagnetic radiation that is at least partly in the visible spectrum (wavelengths from about 3800 Å to about 7800 Å). Devices of reversibly variable transmittance to electromagnetic radiation have been proposed as the variable transmittance element in variable transmittance light-filters, variable reflectance mirrors, and display devices, which employ such light-filters or mirrors in conveying information. These variable transmittance light filters have included windows.

Devices of reversibly variable transmittance to electromagnetic radiation, wherein the transmittance is altered by electrochromic means, are described, for example, by Chang, "Electrochromic and Electrochemichromic Materials and Phenomena," in Non-emissive Electrooptic Displays, A. Kmetz and K. von Willisen, eds. Plenum Press, New York, N.Y. 1976, pp.155-196 (1976) and in various parts of Electrochromism, P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, VCH Publishers, Inc., New York, N.Y. (1995). Numerous electrochromic devices are known in the art. See, e.g., Manos, U.S. Pat. No. 3,451,741; Bredfeldt et al., U.S. Pat. No. 4,090,358; Clecak et al., U.S. Pat. No. 4,139,276; Kissa et al., U.S. Pat. No. 3,453,038; Rogers, U.S. Pat. Nos. 3,652,149, 3,774,988 and 3,873,185; and Jones et al., U.S. Pat. Nos. 3,282,157, 3,282,158, 3,282,160 and 3,283,656.

In addition to these devices, there are commercially available electrochromic devices and associated circuitry, such as those disclosed in U.S. Pat. No. 4,902,108, entitled "SINGLE-COMPARTMENT, SELF-ERASING, SOLUTION-PHASE ELECTROCHROMIC DEVICES SOLUTIONS FOR USE THEREIN, AND USES THEREOF," issued Feb. 20, 1990, to H. J. Byker; Canadian Patent No. 1,300,945, entitled "AUTOMATIC REARVIEW MIRROR SYSTEM FOR AUTOMOTIVE VEHICLES," issued May 19, 1992, to J. H. Bechtel et al.; U.S. Pat. No. 5,128,799, entitled "VARIABLE REFLECTANCE MOTOR VEHICLE MIRROR," issued Jul. 7, 1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled "ELECTRO-OPTIC DEVICE," issued Apr. 13, 1993, to H. J. Byker et al.; U.S. Pat. No. 5,204,778, entitled "CONTROL SYSTEM FOR AUTOMATIC REARVIEW MIRRORS," issued Apr. 20, 1993, to J. H. Bechtel; U.S. Pat. No. 5,278,693, entitled "TINTED SOLUTION-PHASE ELECTROCHROMIC MIRRORS," issued Jan. 11, 1994, to D. A. Theiste et al.; U.S. Pat. No. 5,280,380, entitled "UV-STABILIZED COMPOSITIONS AND METHODS," issued Jan. 18, 1994, to H. J. Byker; U.S. Pat. No. 5,282,077, entitled "VARIABLE REFLECTANCE MIRROR," issued Jan. 25, 1994, to H. J. Byker; U.S. Pat. No. 5,294,376, entitled "BIPYRIDINIUM SALT SOLUTIONS," issued Mar. 15, 1994, to H. J. Byker; U.S. Pat. No. 5,336,448, entitled "ELECTROCHROMIC DEVICES WITH BIPYRIDINIUM SALT SOLUTIONS," issued Aug. 9, 1994, to H. J. Byker; U.S. Pat. No. 5,434,407, entitled "AUTOMATIC REARVIEW MIRROR INCORPORATING LIGHT PIPE," issued Jan. 18, 1995, to F. T. Bauer et al.; U.S. Pat. No. 5,448,397, entitled "OUTSIDE AUTOMATIC REARVIEW MIRROR FOR AUTOMOTIVE VEHICLES," issued Sep. 5, 1995, to W. L. Tonar; and U.S. Pat. No. 5,451,822, entitled "ELECTRONIC CONTROL SYSTEM," issued Sep. 19, 1995, to J. H. Bechtel et al. Each of these patents is commonly assigned with the present invention and the disclosures of each, including the references contained therein, are hereby incorporated herein in their entirety by reference. Such electrochromic devices may be utilized in a fully integrated inside/outside rearview mirror system or as separate inside or outside rearview mirror systems.

FIG. 1 shows a typical electrochromic mirror device 10, having front and rear planar elements 12 and 16, respectively. A transparent conductive coating 14 is placed on the rear face of the front element 12, and another transparent conductive coating 18 is placed on the front face of rear element 16. A reflector (20a, 20b and 20c), typically comprising a silver metal layer 20a covered by a protective copper metal layer 20b, and one or more layers of protective paint 20c, is disposed on the rear face of the rear element 16. For clarity of description of such a structure, the front surface of the front glass element is sometimes referred to as the first surface, and the inside surface of the front glass element is sometimes referred to as the second surface. The inside surface of the rear glass element is sometimes referred to as the third surface, and the back surface of the rear glass element is sometimes referred to as the fourth surface. The front and rear elements are held in a parallel and spaced-apart relationship by seal 22, thereby creating a chamber 26. The electrochromic medium 24 is contained in space 26. The electrochromic medium 24 is in direct contact with transparent electrode layers 14 and 18, through which passes electromagnetic radiation whose intensity is reversibly modulated in the device by a variable voltage or potential applied to electrode layers 14 and 18 through clip contacts and an electronic circuit (not shown).

The electrochromic medium 24 placed in space 26 may include surface-confined, electrodeposition-type or solution-phase-type electrochromic materials and combinations thereof. In an all solution-phase medium, the electrochemical properties of the solvent, optional inert electrolyte, anodic materials, cathodic materials, and any other components that might be present in the solution are preferably such that no significant electrochemical or other changes occur at a potential difference which oxidizes anodic material and reduces the cathodic material other than the electrochemical oxidation of the anodic material, electrochemical reduction of the cathodic material, and the self-erasing reaction between the oxidized form of the anodic material and the reduced form of the cathodic material.

In most cases, when there is no electrical potential difference between transparent conductors 14 and 18, the electrochromic medium 24 in space 26 is essentially colorless or nearly colorless, and incoming light (I_(o)) enters through front element 12, passes through transparent coating 14, electrochromic containing chamber 26, transparent coating 18, rear element 16, and reflects off layer 20a and travels back through the device and out front element 12. Typically, the magnitude of the reflected image (I_(R)) with no electrical potential difference is about 45 percent to about 85 percent of the incident light intensity (I_(o)). The exact value depends on many variables outlined below, such as, for example, the residual reflection (I'_(R)) from the front face of the front element, as well as secondary reflections from the interfaces between: the front element 12 and the front transparent electrode 14, the front transparent electrode 14 and the electrochromic medium 24, the electrochromic medium 24 and the second transparent electrode 18, and the second transparent electrode 18 and the rear element 16. These reflections are well known in the art and are due to the difference in refractive indices between one material and another as the light crosses the interface between the two. If the front element and the back element are not parallel, then the residual reflectance (I'_(R)) or other secondary reflections will not superimpose with the reflected image (I_(R)) from mirror surface 20a, and a double image will appear (where an observer would see what appears to be double (or triple) the number of objects actually present in the reflected image).

There are minimum requirements for the magnitude of the reflected image depending in whether the electrochromic mirrors are placed on the inside or the outside of the vehicle. For example, according to current requirements from most automobile manufacturers, inside mirrors preferably have a high end reflectivity of at least 70 percent, and outside mirrors must have a high end reflectivity of at least 35 percent.

Electrode layers 14 and 18 are connected to electronic circuitry which is effective to electrically energize the electrochromic medium, such that when a potential is applied across the transparent conductors 14 and 18, electrochromic medium in space 26 darkens, such that incident light (I_(o)) is attenuated as the light passes toward the reflector 20a and as it passes back through after being reflected. By adjusting the potential difference between the transparent electrodes, such a device can function as a "gray-scale" device, with continuously variable transmittance over a wide range. For solution-phase electrochromic systems, when the potential between the electrodes is removed or returned to zero, the device spontaneously returns to the same, zero-potential, equilibrium color and transmittance as the device had before the potential was applied. Other electrochromic materials are available for making electrochromic devices. For example, the electrochromic medium may include electrochromic materials that are solid metal oxides, redox active polymers, and hybrid combinations of solution-phase and solid metal oxides or redox active polymers; however, the above-described solution-phase design is typical of most of the electrochromic devices presently in use.

Even before a fourth surface reflector electrochromic mirror was commercially available, various groups researching electrochromic devices had discussed moving the reflector from the fourth surface to the third surface. Such a design has advantages in that it should, theoretically, be easier to manufacture because there are fewer layers to build into a device, i.e., the third surface transparent electrode is not necessary when there is a third surface reflector/electrode. Although this concept was described as early as 1966, no group had commercial success because of the exacting criteria demanded from a workable auto-dimming mirror incorporating a third surface reflector. U.S. Pat. No. 3,280,701, entitled "OPTICALLY VARIABLE ONE-WAY MIRROR," issued Oct. 25, 1966, to J. F. Donnelly et al. has one of the earliest discussions of a third surface reflector for a system using a pH-induced color change to attenuate light.

U.S. Pat. No. 5,066,112, entitled "PERIMETER COATED, ELECTRO-OPTIC MIRROR," issued Nov. 19, 1991, to N. R. Lynam et al., teaches an electro-optic mirror with a conductive coating applied to the perimeter of the front and rear glass elements for concealing the seal. Although a third surface reflector is discussed therein, the materials listed as being useful as a third surface reflector suffer from one or more of the following deficiencies: not having sufficient reflectivity for use as an inside mirror, or not being stable when in contact with a solution-phase electrochromic medium containing at least one solution-phase electrochromic material.

Others have broached the topic of a reflector/electrode disposed in the middle of an all solid state-type device. For example, U.S. Pat. Nos. 4,762,401, 4,973,141, and 5,069,535 to Baucke et al. teach an electrochromic mirror having the following structure: a glass element, a transparent (ITO) electrode, a tungsten oxide electrochromic layer, a solid ion conducting layer, a single layer hydrogen ion-permeable reflector, a solid ion conducting layer, a hydrogen ion storage layer, a catalytic layer, a rear metallic layer, and a back element (representing the conventional third and fourth surface). The reflector is not deposited on the third surface and is not directly in contact with electrochromic materials, certainly not at least one solution-phase electrochromic material and associated medium. Consequently, it is desirable to provide an improved high reflectivity electrochromic rearview mirror having a third surface reflector/electrode in contact with a solution-phase electrochromic medium containing at least one electrochromic material.

In the past, information, images or symbols from displays, such as vacuum fluorescent displays, have been displayed on electrochromic rearview mirrors for motor vehicles with reflective layers on the fourth surface of the mirror. The display is visible to the vehicle occupant by removing all of the reflective layer on a portion of the fourth surface and placing the display in that area. Although this design works adequately due to the transparent conductors on the second and third surface to impart current to the electrochromic medium, presently no design is commercially available which allows a display device to be incorporated into a mirror that has a reflective layer on the third surface. Removing all of the reflective layer on the third surface in the area aligned with the display area or the glare sensor area causes severe residual color problems when the electrochromic medium darkens and clears because, although colorization occurs at the transparent electrode on the second surface, there is no corresponding electrode on the third surface in that corresponding area to balance the charge. As a result, the color generated at the second surface (across from the display area or the glare sensor area) will not darken or clear at the same rate as other areas with balanced electrodes. This color variation is significant and is very aesthetically unappealing to the vehicle occupants.

Similar problems exist for outside rearview mirror assemblies that include signal lights, such as turn signal lights, behind the rear surface of the mirror. Examples of such signal mirrors are disclosed in U.S. Pat. Nos. 5,207,492, 5,361,190, and 5,788,357. By providing a turn signal light in an outside mirror assembly a vehicle, or other vehicles travelling in the blind spot of the subject vehicle, will be more likely to notice when the driver has activated the vehicle's turn signal and thereby attempt to avoid an accident. Such mirror assemblies typically employ a dichroic mirror and a plurality of red LEDs mounted behind the mirror as the signal light source. The dichroic mirror includes a glass substrate and a dichroic reflective coating provided on the rear surface of the glass plate that transmits the red light generated by the LEDs as well as infrared radiation while reflecting all light and radiation having wavelengths less than that of red light. By utilizing a dichroic mirror, such mirror assemblies hide the LEDs when not in use to provide the general appearance of a typical rearview mirror, and allow the red light from such LEDs to pass through the dichroic mirror and be visible to drivers of vehicles behind and to the side of the vehicle in which such a mirror assembly is mounted.

In daylight, the intensity of the LEDs must be relatively high to enable those in other to vehicles to readily notice the signal lights. Because the image reflected toward the driver is also relatively high in daylight, the brightness of the LEDs is not overly distracting. However, at night the same LED intensity could be very distracting, and hence, potentially hazardous. To avoid this problem, a day/night sensing circuit is mounted in the signal light subassembly behind the dichroic mirror to sense whether it is daytime or nighttime and toggle the intensity of the LEDs between two different intensity levels. The sensor employed in the day/night sensing circuit is most sensitive to red and infrared light so as to more easily distinguish between daylight conditions and the bright glare from the headlights of a vehicle approaching from the rear. Hence, the sensor may be mounted behind the dichroic coating on the dichroic mirror.

The dichroic mirrors used in the above-described outside mirror assemblies suffer from the same problems of many outside mirror assemblies in that their reflectance cannot be dynamically varied to reduce nighttime glare from the headlights of other vehicles.

Although outside mirror assemblies exist that include signal lights and other outside mirror assemblies exist that include electrochromic mirrors, signal lights have not been provided in mirror assemblies having an electrochromic mirror because the dichroic coating needed to hide the LEDs of the signal light typically cannot be applied to an electrochromic mirror, particularly those mirrors that employ a third surface reflector/electrode.

One approach to the above problems relating to mounting a signal light or information <X display to the rear of a third surface electrochromic mirror is disclosed in U.S. patent application Ser. No. 09/175,984 filed on Oct. 20, 1998, and U.S. Pat. No. 5,825,527. These patents collectively disclose a solution to the above problems whereby discrete portions of the reflector/electrode are etched away from the third surface so as to form a fine grid of spaced-apart and parallel lines of reflector/electrode material in only those regions in front of the display, sensors, or signal lights. The spaced-apart reflector/electrode lines are sufficient to create the necessary conduction paths in the display/signal light regions so that the electrochromic medium will exhibit satisfactory coloration in those regions while also enabling some reflection in those regions, thereby providing a more ascetically pleasing appearance. Nevertheless, due to the presence of the "stripes" in front of the display, there remained a need for a solution to the above-noted problems that provides for an even better ascetic appearance.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to solve the above problems by providing an electrochromic rearview mirror assembly that includes a third surface reflector/electrode that provides a continuous layer of electrically conductive material across the entire visible surface of the rear element of the mirror, even those regions that lie in front of a light source, such as a signal light or information display that is positioned behind the electrochromic mirror. Yet another aspect of the present invention is to provide an electrochromic mirror having a third surface reflector/electrode that is at least partially transmissive at least in regions in front of a light source, such as a display or signal light.

To achieve these and other aspects and advantages, the electrochromic mirror according to the present invention comprises front and rear spaced elements, each having front and rear surfaces and being sealably bonded together in a spaced-apart relationship to define a chamber; a transparent first electrode including a layer of conductive material disposed on the rear surface of the front element; at least one solution-phase electrochromic material contained within the chamber; and a second electrode overlying the front surface of the rear element in contact with the electrochromic material. The second electrode includes a layer of highly reflective material and a coating of electrically conductive material that is at least partially transmissive and is disposed over substantially all of the front surface of the rear element. The second electrode further includes a region in front of the light source that is disposed behind the electrochromic mirror that is at least partially transmissive.

An additional aspect of the present invention is to provide a third surface reflector/electrode (i.e., second electrode) that is at least partially reflective in those regions in front of the light source so as to provide an ascetically pleasing appearance. To achieve this and other aspects and advantages, either a thin layer of the highly reflective material may be applied to those regions in front of the light source or the electrically conductive coating underlying the highly reflective layer may be made of materials that are not only electrically conductive, but also partially reflective and partially transmissive.

Still another aspect of the present invention is to provide a coating for the third surface of an electrochromic mirror that functions as an electrode and as a reflector while allowing light having wavelengths corresponding to a light source to be transmitted through the mirror. To achieve this and other aspects and advantages, the electrode of the present invention comprises a first layer of a first material having a relatively high refractive index; a second layer of a second material having a relatively low refractive index disposed on the first layer; and a third layer of a third material disposed on the second layer. The third layer may have a relatively high refractive index. Either the third material is electrically conductive or a fourth layer of an electrically conductive material is disposed on the third layer. If the first, second, and third layers provide sufficient reflectivity, such a fourth layer may be made of a transparent conductive material. If not, the fourth layer may be made of a highly reflective material.

These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an enlarged cross-sectional view of a prior art electrochromic mirror assembly;

FIG. 2 is a front elevational view schematically illustrating an inside/outside electrochromic rearview mirror system for motor vehicles, where the inside and outside mirrors incorporate the mirror assembly of the present invention;

FIG. 3 is an enlarged cross-sectional view of the inside electrochromic rearview mirror incorporating a third surface reflector/electrode illustrated in FIG. 2, taken on the line 3-3' thereof;

FIG. 4 is an enlarged cross-sectional view of an electrochromic mirror incorporating an alternate embodiment of a third surface reflector/electrode according to the present invention;

FIG. 5a is an enlarged cross-sectional view of an electrochromic mirror having an improved arrangement for applying a drive potential to the transparent conductor on the second surface of the mirror;

FIG. 5b is an enlarged top view of the third surface reflector of FIG. 5a;

FIG. 6 is an enlarged cross-sectional view of an electrochromic mirror using a cured and machine-milled epoxy seal to hold the transparent elements in a spaced-apart relationship;

FIGS. 7A-7G are partial cross-sectional views of alternative constructions of the electrochromic mirror according to the present invention as taken along line 7-7' shown in FIG. 2;

FIG. 8 is a perspective view of an outside automatic rearview mirror including a signal light and an electrical circuit diagram in block form of an outside rearview mirror assembly constructed in accordance with the present invention;

FIG. 9 is a front elevational view of a signal light subassembly that may be used in the outside mirror assembly of the present invention;

FIG. 10 is a partial cross-sectional view taken along line 10-10' of FIG. 8 illustrating one construction of the outside rearview mirror of the present invention; and

FIG. 11 is a pictorial representation of two vehicles, one of which includes the signal mirror of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows a front elevational view schematically illustrating an inside mirror assembly 110 and two outside rearview mirror assemblies 111a and 111b for the driver-side and passenger-side, respectively, all of which are adapted to be installed on a motor vehicle in a conventional manner and where the mirrors face the rear of the vehicle and can be viewed by the driver of the vehicle to provide a rearward view. Inside mirror assembly 110 and outside rearview mirror assemblies 111a and 111b may incorporate light-sensing electronic circuitry of the type illustrated and described in the above-referenced Canadian Patent No. 1,300,945, U.S. Pat. No. 5,204,778, or U.S. Pat. No. 5,451,822, and other circuits capable of sensing glare and ambient light and supplying a drive voltage to the electrochromic element. Mirror assemblies 110, 111a, and 111b are essentially identical in that like numbers identify components of the inside and outside mirrors. These components may be slightly different in configuration, but function in substantially the same manner and obtain substantially the same results as similarly numbered components. For example, the shape of the front glass element of inside mirror 110 is generally longer and narrower than outside mirrors 111a and 111b. There are also some different performance standards placed on inside mirror 110 compared with outside mirrors 111a and 111b. For example, inside mirror 110 generally, when fully cleared, should have a reflectance value of about 70 percent to about 85 percent or higher, whereas the outside mirrors often have a reflectance of about 50 percent to about 65 percent. Also, in the United States (as supplied by the automobile manufacturers), the passenger-side mirror 111b typically has a spherically bent or convex shape, whereas the driver-side mirror 111a and inside mirror 110 presently must be flat. In Europe, the driver-side mirror 111a is commonly flat or aspheric, whereas the passenger-side mirror 111b has a convex shape. In Japan, both outside mirrors have a convex shape. The following description is generally applicable to all mirror assemblies of the present invention.

FIG. 3 shows a cross-sectional view of mirror assembly 110 having a front transparent element 112 having a front surface 112a and a rear surface 112b, and a rear element 114 having a front surface 114a and a rear surface 114b. For clarity of description of such a structure, the following designations will be used hereinafter. The front surface 112a of the front glass element will be referred to as the first surface, and the back surface 112b of the front glass element as the second surface. The front surface 114a of the rear glass element will be referred to as the third surface, and the back surface 114b of the rear glass element as the fourth surface. A chamber 125 is defined by a layer of transparent conductor 128 (disposed on second surface 112b), a reflector/electrode 120 (disposed on third surface 114a), and an inner circumferential wall 132 of sealing member 116. An electrochromic medium 126 is contained within chamber 125.

Front transparent element 112 may be any material which is transparent and has is sufficient strength to be able to operate in the conditions, e.g., varying temperatures and pressures, commonly found in the automotive environment. Front element 112 may comprise any type of borosilicate glass, soda lime glass, float glass, or any other material, such as, for example, a polymer or plastic, that is transparent in the visible region of the electromagnetic spectrum. Front element 112 is preferably a sheet of glass. The rear element must meet the operational conditions outlined above, except that it does not need to be transparent, and therefore may comprise polymers, metals, glass, ceramics, and preferably is a sheet of glass.

The coatings of the third surface 114a are sealably bonded to the coatings on the second surface 112b in a spaced-apart and parallel relationship by a seal member 116 disposed near the outer perimeter of both second surface 112b and third surface 114a. Seal member 116 may be any material that is capable of adhesively bonding the coatings on the second surface 112b to the coatings on the third surface 114a to seal the perimeter such that electrochromic material 126 does not leak from chamber 125. Optionally, the layer of transparent conductive coating 128 and the layer of reflector/electrode 120 may be removed over a portion where the seal member is disposed (not the entire portion, otherwise the drive potential could not be applied to the two coatings). In such a case, seal member 116 must bond well to glass.

The performance requirements for a perimeter seal member 116 used in an electrochromic device are similar to those for a perimeter seal used in a liquid crystal device (LCD), which are well known in the art. The seal must have good adhesion to glass, metals and metal oxides; must have low permeabilities for oxygen, moisture vapor, and other detrimental vapors and gases; and must not interact with or poison the electrochromic or liquid crystal material it is meant to contain and protect. The perimeter seal can be applied by means commonly used in the LCD industry, such as by silk-screening or dispensing. Totally hermetic seals, such as those made with glass frit or solder glass, can be used, but the high temperatures involved in processing (usually near 450° C.) this type of seal can cause numerous problems, such as glass substrate warpage, changes in the properties of transparent conductive electrode, and oxidation or degradation of the reflector. Because of their lower processing temperatures, thermoplastic, thermosetting or UV curing organic sealing resins are preferred. Such organic resin sealing systems for LCDs are described in U.S. Pat. Nos. 4,297,401, 4,418,102, 4,695,490, 5,596,023, and 5,596,024. Because of their excellent adhesion to glass, low oxygen permeability and good solvent resistance, epoxy-based organic sealing resins are preferred. These epoxy resin seals may be UV curing, such as described in U.S. Pat. No. 4,297,401, or thermally curing, such as with mixtures of liquid epoxy resin with liquid polyamide resin or dicyandiamide, or they can be homopolymerized. The epoxy resin may contain fillers or thickeners to reduce flow and shrinkage such as fumed silica, silica, mica, clay, calcium carbonate, alumina, etc., and/or pigments to add color. Fillers pretreated with hydrophobic or silane surface treatments are preferred. Cured resin crosslink density can be controlled by use of mixtures of mono-functional, di-functional, and multi-functional epoxy resins and curing agents. Additives such as silanes or titanates can be used to improve the seal's hydrolytic stability, and spacers such as glass beads or rods can be used to control final seal thickness and substrate spacing. Suitable epoxy resins for use in a perimeter seal member 116 include, but are not limited to: "EPON RESIN" 813, 825, 826, 828, 830, 834, 862, 1001F, 1002F, 2012, DPS-155, 164, 1031, 1074, 58005, 58006, 58034, 58901, 871, 872, and DPL-862 available from Shell Chemical Co., Houston, Tex.; "ARALITE" GY 6010, GY 6020, CY 9579, GT 7071, XU 248, EPN 1139, EPN 1138, PY 307, ECN 1235, ECN 1273, ECN 1280, MT 0163, MY 720, MY 0500, MY 0510, and PT 810 available from Ciba Geigy, Hawthorne, N.Y.; and "D.E.R." 331, 317, 361, 383, 661, 662, 667, 732, 736, "D.E.N." 431, 438, 439 and 444 available from Dow Chemical Co., Midland, Mich. Suitable epoxy curing agents include V-15, V-25, and V-40 polyamides from Shell Chemical Co.; "AJICURE" PN-23, PN-34, and VDH available from Ajinomoto Co., Tokyo, Japan; "CUREZOL" AMZ, 2MZ, 2E4MZ, C11Z, C17Z, 2PZ, 21Z, and 2P4MZ available from Shikoku Fine Chemicals, Tokyo, Japan; "ERISYS" DDA or DDA accelerated with U-405, 24EMI, U-410, and U415 available from CVC Specialty Chemicals, Maple Shade, N.J.; and "AMICURE" PACM, 352, CG, CG-325, and CG-1200 available from Air Products, Allentown, Pa. Suitable fillers include fumed silica such as "CAB-O-SIL" L-90, LM-130, LM-5, PTG, M-5, MS-7, MS-55, TS-720, HS-5, and EH-5 available from Cabot Corporation, Tuscola, Ill.; "AEROSIL" R972, R974, R805, R812, R812 S, R202, US204, and US206 available from Degussa, Akron, Ohio. Suitable clay fillers include BUCA, CATALPO, ASP NC, SATINTONE 5, SATINTONE SP-33, TRANSLINK 37, TRANSLINK 77, TRANSLINK 445, and TRANSLINK 555 available from Engelhard Corporation, Edison, N.J. Suitable silica fillers are SILCRON G-130, G-300, G-100-T, and G-100 available from SCM Chemicals, Baltimore, Md. Suitable silane coupling agents to improve the seal's hydrolytic stability are Z-6020, Z-6030, Z-6032, Z-6040, Z-6075, and Z-6076 available from Dow Corning Corporation, Midland, Mich. Suitable precision glass microbead spacers are available in an assortment of sizes from Duke Scientific, Palo Alto, Calif.

The layer of a transparent electrically conductive material 128 is deposited on the second surface 112b to act as an electrode. Transparent conductive material 128 may be any material which bonds well to front element 112, is resistant to corrosion to any materials within the electrochromic device, resistant to corrosion by the atmosphere, has minimal diffuse or specular reflectance, high light transmission, near neutral coloration, and good electrical conductance. Transparent conductive material 128 may be fluorine-doped tin oxide, doped zinc oxide, zinc-oped indium oxide, tin-doped indium oxide (ITO), ITO/metal/ITO (IMI) as disclosed in "Transparent Conductive Multilayer-Systems for FPD Applications," by J. Stollenwerk, B. Ocker, K. H. Kretschmer of LEYBOLD AG, Alzenau, Germany, the materials described in above-referenced U.S. Pat. No. 5,202,787, such as TEC 20 or TEC 15, available from Libbey Owens-Ford Co. of Toledo, Ohio, or other transparent conductors. Generally, the conductance of transparent conductive material 128 will depend on its thickness and composition. IMI generally has superior conductivity compared with the other materials. IMI is, however, known to undergo more rapid environmental degradation and suffer from interlayer delamination. The thickness of the various layers in the IMI structure may vary, but generally the thickness of the first ITO layer ranges from about 10 Å to about 200 Å, the metal ranges from about 10 Å to about 200 Å, and the second layer of ITO ranges from about 10 Å to about 200 Å. If desired, an optional layer or layers of a color suppression material 130 may be deposited between transparent conductive material 128 and the second surface 112b to suppress the reflection of any unwanted portions of the electromagnetic spectrum.

In accordance with the present invention, a combination reflector/electrode 120 is disposed on third surface 114a. Reflector/electrode 120 comprises at least one layer of a highly reflective material 121 which serves as a mirror reflectance layer and also forms an integral electrode in contact with and in a chemically and electrochemically stable relationship with any constituents in an electrochromic medium. As stated above, the conventional method of building electrochromic devices was to incorporate a transparent conductive material on the third surface as an electrode, and place a reflector on the fourth surface. By combining the "reflector" and "electrode" and placing both on the third surface, several unexpected advantages arise which not only make the device manufacture less complex, but also allow the device to operate with higher performance. The following will outline the exemplary advantages of the combined reflector/electrode of the present invention.

First, the combined reflector/electrode 120 on the third surface generally has higher conductance than a conventional transparent electrode and previously used reflector/electrodes, which will allow greater design flexibility. One can either change the composition of the transparent conductive electrode on the second surface to one that has lower conductance (being cheaper and easier to produce and manufacture) while maintaining coloration speeds similar to that obtainable with a fourth surface reflector device, while at the same time decreasing substantially the overall cost and time to produce the electrochromic device. If, however, performance of a particular design is of utmost importance, a moderate to high conductance transparent electrode can be used on the second surface, such as, for example, ITO, IMI, etc. The combination of a high conductance (i.e., less than 250 Ω/□, preferably less than 15 Ω/□) reflector/electrode on the third surface and a high conductance transparent electrode on the second surface will not only produce an electrochromic device with more even overall coloration, but will also allow for increased speed of coloration and clearing. Furthermore, in fourth surface reflector mirror assemblies there are two transparent electrodes with relatively low conductance, and in previously used third surface reflector mirrors there is a transparent electrode and a reflector/electrode with relatively low conductance and, as such, a long buss bar on the front and rear element to bring current in and out is necessary to ensure adequate coloring speed. The third surface reflector/electrode of the present invention has a higher conductance and therefore has a very even voltage or potential distribution across the conductive surface, even with a small or irregular contact area. Thus, the present invention provides greater design flexibility by allowing the electrical contact for the third surface electrode to be very small while still maintaining adequate coloring speed.

Second, a third surface reflector/electrode helps improve the image being viewed through the mirror. FIG. 1 shows how light travels through a conventional fourth surface reflector device. In the fourth surface reflector, the light travels through: the first glass element, the transparent conductive electrode on the second surface, the electrochromic media, the transparent conductive electrode on the third surface, and the second glass element, before being reflected by the fourth surface reflector. Both transparent conductive electrodes exhibit highly specular transmittance but also possess diffuse transmittance and reflective components, whereas the reflective layer utilized in any electrochromic mirror is chosen primarily for its specular reflectance. By diffuse reflectance or transmittance component, we mean a material which reflects or transmits a portion of any light impinging on it according to Lambert's law whereby the light rays are spread-about or scattered. By specular reflectance or transmittance component, we mean a material which reflects or transmits light impinging on it according to Snell's laws of reflection or refraction. In practical terms, diffuse reflectors and transmitters M tend to slightly blur images, whereas specular reflectors show a crisp, clear image. Therefore, light traveling through a mirror having a device with a fourth surface reflector has two partial diffuse reflectors (on the second and third surface) which tend to blur the image, and a device with a third surface reflector/electrode of the present invention only has one diffuse reflector (on the second surface).

Additionally, because the transparent electrodes act as partial diffuse transmitters, and the farther away the diffuse transmitter is from the reflecting surface the more severe the blurring becomes, a mirror with a fourth surface reflector appears significantly more hazy than a mirror with a third surface reflector. For example, in the fourth surface reflector shown in FIG. 1, the diffuse transmitter on the second surface is separated from the reflector by the electrochromic material, the second conductive electrode, and the second glass element. The diffuse transmitter on the third surface is separated from the reflector by the second glass element. By incorporating a combined reflector/electrode on the third surface in accordance with the present invention, one of the diffuse transmitters is removed, and the distance between the reflector and the remaining diffuse transmitter is closer by the thickness of the rear glass element. Therefore, the third surface metal reflector/electrode of the present invention provides an electrochromic mirror with a superior viewing image.

Finally, a third surface metal reflector/electrode improves the ability to reduce double imaging in an electrochromic mirror. As stated above, there are several interfaces where reflections can occur. Some of these reflections can be significantly reduced with color suppression or anti-reflective coatings; however, the most significant "double imaging" reflections are caused by misalignment of the first surface and the surface containing the reflector, and the most reproducible way of minimizing the impact of this reflection is by ensuring both glass elements are parallel. Presently, convex glass is often used for the passenger side outside mirror and aspheric glass is sometimes used for the driver side outside mirror to increase the field of view and reduce potential blind spots. However, it is difficult to reproducibly bend successive elements of glass having identical radii of curvature. Therefore, when building an electrochromic mirror, the front glass element and the rear glass element may not be perfectly parallel (do not have identical radii of curvature), and therefore, the otherwise controlled double imaging problems become much more pronounced. By incorporating a combined reflector electrode on the third surface of the device in accordance with the present invention, light does not have to travel through the rear glass element before being reflected, and any double imaging that occurs from the elements being out of parallel will be significantly reduced.

It is desirable in the construction of outside rearview mirrors to incorporate thinner glass in order to decrease the overall weight of the mirror so that the mechanisms used to manipulate the orientation of the mirror are not overloaded. Decreasing the weight of the device also improves the dynamic stability of the mirror assembly when exposed to vibrations. Heretofore, no electrochromic mirrors incorporating a solution-phase electrochromic medium and two thin glass elements have been commercially available, because thin glass suffers from being flexible and prone to warpage or breakage, especially when exposed to extreme environments. This problem is substantially improved by using an improved electrochromic device incorporating two thin glass elements having an improved gel material. This improved to device is disclosed in commonly assigned U.S. Pat. No. 5,940,201 entitled "AN ELECTROCHROMIC MIRROR WITH TWO THIN GLASS ELEMENTS AND A GELLED ELECTROCHROMIC MEDIUM," filed on Apr. 2, 1997. The entire disclosure, including the references contained therein, of this U.S. patent is incorporated herein by reference. The addition of the combined reflector/electrode onto the third surface of the device further helps remove any residual double imaging resulting from the two glass elements being out of parallel.

The most important factors for obtaining a reliable electrochromic mirror having a third surface reflector/electrode 120 are that the reflector/electrode have sufficient reflectance and that the mirror incorporating the reflector/electrode has adequate operational life. Regarding reflectance, the automobile manufacturers prefer a highly reflective mirror for the inside mirror having a reflectivity of at least 60 percent, whereas the reflectivity requirements for an outside mirror are less stringent and generally must be at least 35 percent.

To produce an electrochromic mirror with 70 percent reflectance, the reflector must have a reflectance higher than 70 percent because the electrochromic medium in front of the reflector reduces the reflectance from the reflector interface as compared to having the reflector in air due to the medium having a higher index of refraction as compared to air. Also, the glass, the transparent electrode, and the electrochromic medium even in its clear state are slightly light absorbing. Typically, if an overall reflectance of 65 percent is desired, the reflector must have a reflectance of about 75 percent.

Regarding operational life, the layer or layers that comprise the reflector/electrode 120 must have adequate bond strength to the peripheral seal, the outermost layer must have good shelf life between the time it is coated and the time the mirror is assembled, the layer or layers must be resistant to atmospheric and electrical contact corrosion, and must bond well to the glass surface or to other layers disposed beneath it, e.g., the base or intermediate layer (122 or 123, respectively). The overall sheet resistance for the reflector/electrode 120 may range from about 0.01 Ω/□ to about 100 Ω/□ and preferably ranges from about 0.2 Ω/□ to about 25 Ω/□. As will be discussed in more detail below, improved electrical interconnections using a portion of the third surface reflector/electrode as a high conductance contact or buss bar for the second surface transparent conductive electrode may be utilized when the conductance of the third surface reflector/electrode is below about 2 •/□.

Referring to FIG. 3 for one embodiment of the present invention, a reflector/electrode that is made from a single layer of a highly reflective silver or silver alloy 121 is provided that is in contact with at least one solution-phase electrochromic material. The layer of silver or silver alloy covers the entire third surface 114a of second element 114. The highly reflective silver alloy means a homogeneous or non-homogeneous mixture of silver and one or more metals, or an unsaturated, saturated, or supersaturated solid solution of silver and one or more metals. The thickness of highly reflective layer 121 ranges from about 50 Å to about 2000 Å, and more preferably from about 200 Å to about 1000 Å. If highly reflective layer 121 is disposed directly to the glass surface, it is preferred that the glass surface be treated by plasma discharge to improve adhesion.

Table 1 shows the relevant properties for a number of different metals that have been proposed for third surface reflectors as compared with the materials suitable for the reflector/electrode 120 of the present invention. The only materials in Table 1 having reflectance properties suitable for use as a third surface reflector/electrode in contact with at least one solution-phase electrochromic material for an inside electrochromic mirror for a motor vehicle are aluminum, silver, and silver alloys. Aluminum performs very poorly when in contact with solution-phase material(s) in the electrochromic medium because aluminum reacts with or is corroded by these materials. The reacted or corroded aluminum is non-reflective and non-conductive and will typically dissolve off, flake off, or delaminate from the glass surface. Silver is more stable than aluminum but can fail when deposited over the entire third surface because it does not have long shelf life and is not resistant to electrical contact corrosion when exposed to the environmental extremes found in the motor vehicle environment. These environmental extremes include temperatures ranging from about -40° C. to about 85° C., and humidities ranging from about 0 percent to about 100 percent. Further, mirrors must survive at these temperatures and humidities for coloration cycle lives up to 100,000 cycles. The other prior art materials (silver/copper, chromium, stainless steel, rhodium, platinum, palladium, Incone®, copper, or titanium) suffer from any one of a number of deficiencies such as: very poor color neutrality (silver/copper and copper); poor reflectance (chromium, stainless steel, rhodium, molybdenum, platinum, palladium, Incone®, and titanium); poor cleanability (chromium); or poor electrical contact stability (chromium, stainless steel and molybdenum).

When silver is alloyed with certain materials to produce a third surface reflector/electrode, the deficiencies associated with silver metal and aluminum metal can be overcome. Suitable materials for the reflective layer are alloys of silver/palladium, silver/gold, silver/platinum, silver/rhodium, silver/titanium, etc. The amount of the solute material, i.e., palladium, gold, etc., can vary. As can be seen from Table 1, the silver alloys surprisingly retain the high reflectance and low sheet resistance properties of silver, while simultaneously improving their contact stability, shelf life, and also increasing their window of potential stability when used as electrodes in propylene carbonate containing 0.2 molar tetraethylammonium tetrafluoroborate. The presently preferred materials for highly reflective layer 121 are silver/gold, silver/platinum, and silver/palladium.

More typically, reflector/electrode 120 has, in addition to the layer of a highly reflective alloy 121, an optional base layer of a conductive metal or alloy 122 deposited directly on the third surface 114a. There may also be an optional intermediate layer of a conductive metal or alloy 123 disposed between the layer of highly reflective material 121 and the base coat 122. If reflector/electrode 120 includes more than one layer, there should not be galvanic corrosion between the two metals or alloys. If optional base layer 122 is deposited between the highly reflective layer 121 and the glass element 114, it should be environmentally rugged, e.g., bond well to the third (glass) surface 114a and to highly reflective layer 121, and maintain this bond when the seal 116 is bonded to the reflective layer. Base layer 122 should have a thickness from about 50 Å to about 2000 Å, and more preferably from about 100 Å to about 1000 Å. Suitable materials for the base layer 122 are chromium, stainless steel, titanium, and alloys of chromium/molybdenum/nickel, molybdenum, and nickel-based alloys (commonly referred to as Incone®, available from Castle Metals, Chicago, Ill.). The main constituents of Incone® are nickel which may range from 52 percent to 76 percent (Incone® 617 and 600, respectfully), iron which may range from 1.5 percent to 18.5 percent (Incone® 617 and Incone® 718, respectfully), and chromium which may range from 15 percent to 23 percent (Incone®600 and Incone® 601, respectfully). Incone® 617 having 52 percent nickel, 1.5 percent iron, 22 percent chromium, and typical "other" constituents including 12.5 percent cobalt, 9.0 percent molybdenum, and 1.2 percent aluminum was used in the present examples.

In some instances it is desirable to provide an optional intermediate layer 123 between the highly reflective layer 121 and the base layer 122 in case the material of layer 121 does not adhere well to the material of layer 122 or there are any adverse interactions between the materials, e.g., galvanic corrosion. If used, intermediate layer 123 should exhibit environmental ruggedness, e.g., bond well to the base layer 122 and to the highly reflective layer 121, and maintain this bond when the seal member 116 is bonded to the highly reflective layer 121. The thickness of intermediate layer 123 ranges from about 10 Å to about 2000 Å, and more preferably from about 100 Å to about 1000 Å. Suitable materials for the optional intermediate layer 123 are molybdenum, rhodium, stainless steel, titanium, copper, nickel, and platinum. Reference is made to examples 1 and 2 to show how the insertion of a rhodium intermediate layer between a chromium base layer and a silver or silver alloy reflective layer increases the time to failure in copper-accelerated acetic acid-salt spray (CASS) by a factor of 10. Example 4 shows how the insertion of a molybdenum intermediate layer between a chromium base layer and a silver alloy having a molybdenum flash over-coat layer increases the time to failure in CASS by a factor of 12.

Finally, it is sometimes desirable to provide an optional flash over-coat 124 over highly reflective layer 121, such that it (and not the highly reflective layer 121) contacts the electrochromic medium. This flash over-coat layer 124 must have stable behavior as an electrode, it must have good shelf life, it must bond well to the highly reflective layer 121, and maintain this bond when the seal member 116 is bonded thereto. It must be sufficiently thin, such that it does not completely block the reflectivity of highly reflective layer 121. In accordance with another embodiment of the present invention, when a very thin flash over-coat 124 is placed over the highly reflecting layer, then the highly reflective layer 121 may be silver metal or a silver alloy because the flash layer protects the highly reflective layer while still allowing the highly reflecting layer 121 to contribute to the reflectivity of the mirror. In such cases, a thin (between about 25 Å and about 300 Å) layer of rhodium, platinum, or molybdenum is deposited over the highly reflective layer 121.

It is preferred but not essential that the third surface reflector/electrode 120 be maintained as the cathode in the circuitry because this eliminates the possibility of anodic dissolution or anodic corrosion that might occur if the reflector/electrode was used as the anode. Although as can be seen in Table 1, if certain silver alloys are used, the positive potential limit of stability extends out far enough, e.g., 1.2 V, that the silver alloy reflector/electrode could safely be used as the anode in contact with at least one solution-phase electrochromic material.

                                      TABLE 1                                      __________________________________________________________________________          White Light                                                                          Reflectance                                                                               Negative Potential Limit                                                                  Positive Potential Limit                           Reflectance                                                                          In Device                                                                            Contact                                                                             of Window of Potential                                                                    Window of Potential                           Metal                                                                               In Air                                                                               (%)   Stability                                                                           Stability (V)                                                                             Stability (V)                                 __________________________________________________________________________     Al   >92   N/A   very poor                                                                           N/A        N/A                                           Cr   65    N/A   poor N/A        N/A                                           Stainless                                                                           60    N/A   good N/A        N/A                                           Steel                                                                          Rh   75    N/A   very good                                                                           N/A        N/A                                           Pt   72    N/A   very good                                                                           N/A        N/A                                           Inconel                                                                             55    N/A   N/A  N/A        N/A                                           Ag   97    84    fair -2.29      0.86                                          Ag2.7Pd                                                                             93    81    good -2.26      0.87                                          Ag10Pd                                                                              80    68    good -2.05      0.97                                          Ag6Pt                                                                               92    80    good -1.66*     0.91                                          Ag6Au                                                                               96    84    good -2.25      0.98                                          Ag15Au                                                                              94    82    good -2.3       1.2                                           __________________________________________________________________________      *This number is suspect because the test was run in propylene carbonate        containing some water.                                                   

The various layers of reflector/electrode 120 can be deposited by a variety of deposition procedures, such as RF and DC sputtering, e-beam evaporation, chemical vapor deposition, electrodeposition, etc., that will be known to those skilled in the art. The preferred alloys are preferably deposited by sputtering (RF or DC) a target of the desired alloy or by sputtering separate targets of the individual metals that make up the desired alloy, such that the metals mix during the deposition process and the desired alloy is produced when the mixed metals deposit and solidify on the substrate surface.

In another embodiment, the reflector/electrode 120 shown in FIG. 4 has at least two layers (121 and 122), where at least one layer of a base material 122 covers substantially the entire portion of the third surface 114a and at least one layer of a highly reflective material 121 covers the inner section of the third surface 114a, but does not cover the peripheral edge portion 125 where seal member 116 is disposed. Peripheral portion 125 may be created by masking that portion of layer 122 during deposition of the layer of highly reflective material 121, or the layer of highly reflective material may be deposited over the entire third surface and subsequently removed or partially removed in the peripheral portion. The masking of layer 122 may be accomplished by use of a physical mask or through other well-known techniques, such as photolithography and the like. Alternatively, layer 122 may be partially removed in the peripheral portion by a variety of techniques, such as, for example, by etching (laser, chemical, or otherwise), mechanical scraping, sandblasting, or otherwise. Laser etching is the presently preferred method because of its accuracy, speed, and control. Partial removal is preferably accomplished by laser etching in a pattern where enough metal is removed to allow the seal member 116 to bond directly to the third surface 114a while leaving enough metal in this area such that the conductance in this area is not significantly reduced.

Although the various embodiments described below are preferred to enable a light source such as a signal light or display to be seen from behind the mirror, the grating-type structure disclosed in U.S. patent application Ser. No. 09/175,984 filed on Oct. 20, 1998, and U.S. Pat. No. 5,825,527 may also be used. Both of these patent documents are commonly assigned with the present invention and the disclosures of each, including the references contained therein, are incorporated herein in their entirety by reference.

In addition, an optional intermediate layer of a conductive material 123 may be placed over the entire area of third surface 114a and disposed between the highly reflective layer 121 and the base layer 122, or it may be placed only under the area covered by layer 121, i.e., not in peripheral edge portion 125. If this optional intermediate layer is utilized, it can cover the entire area of third surface 114a or it may be masked or removed from the peripheral edge portion as discussed above.

An optional flash over-coat layer 124 may be coated over the highly reflective layer 121. The highly reflective layer 121, the optional intermediate layer 123, and the base layer 122 preferably have properties similar to that described above, except that the layer of highly reflective material 121 need not bond well to the epoxy seal, since it is removed in the peripheral portion where the seal member 116 is placed. Because the interaction with the epoxy seal is removed, silver metal itself, in addition to the alloys of silver described above, will function as the highly reflective layer. Alternatively, an adhesion promoter can be added to the sealing material which enhances adhesion to silver or silver alloys and the highly reflective layer can be deposited over most of the third surface including substantial portions under the seal area. Such adhesion promoters are disclosed in U.S. patent application Ser. No. 09/158,423, entitled "IMPROVED SEAL FOR ELECTROCHROMIC DEVICES," the disclosure of which is incorporated herein by reference.

Referring again to FIG. 3, chamber 125, defined by transparent conductor 128 (disposed on front element rear surface 112b), reflector/electrode 120 (disposed on rear element front surface 114a), and an inner circumferential wall 132 of sealing member 116, contains an electrochromic medium 126. Electrochromic medium 126 is capable of attenuating light traveling therethrough and has at least one solution-phase electrochromic material in intimate contact with reflector/electrode 120 and at least one additional electroactive material that may be solution-phase, surface-confined, or one that plates out onto a surface. However, the presently preferred media are solution-phase redox electrochromics, such as those disclosed in above-referenced U.S. Pat. Nos. 4,902,108, 5,128,799, 5,278,693, 5,280,380, 5,282,077, 5,294,376, and 5,336,448. Co-filed U.S. patent application Ser. No. 08/832,596, now U.S. Pat. No. 6,020,987, entitled "AN IMPROVED ELECTROCHROMIC MEDIUM CAPABLE OF PRODUCING A PRE-SELECTED COLOR" discloses electrochromic media that are perceived to be gray throughout their normal range of operation. The entire disclosure of this application is hereby incorporated herein by reference. If a solution-phase electrochromic medium is utilized, it may be inserted into chamber 125 through a sealable fill port 142 through well-known techniques, such as vacuum backfilling and the like.

A resistive heater 138, disposed on the fourth glass surface 114b, may optionally be a layer of ITO, fluorine-doped tin oxide, or may be other heater layers or structures well known in the art. Electrically conductive spring clips 134a and 134b are placed on the coated glass sheets (112 and 114) to make electrical contact with the exposed areas of the transparent conductive coating 128 (clip 134b) and the third surface reflector/electrode 120 (clip 134a). Suitable electrical conductors (not shown) may be soldered or otherwise connected to the spring clips (134a and 134b) so that a desired voltage may be applied to the device from a suitable power source.

An electrical circuit 150, such as those taught in the above-referenced Canadian Patent No. 1,300945 and U.S. Pat. Nos. 5,204,778, 5,434,407, and 5,451,822, is connected to and allows control of the potential to be applied across reflector/electrode 120 and transparent electrode 128, such that electrochromic medium 126 will darken and thereby attenuate various amounts of light traveling therethrough and thus vary the reflectance of the mirror containing electrochromic medium 126.

As stated above, the low resistance of reflector/electrode 120 allows greater design flexibility by allowing the electrical contact for the third surface reflector/electrode to be small while maintaining adequate coloring speed. This flexibility extends to improving the interconnection techniques to the layer of transparent conductive material 128 on the second surface 112b. Referring now to FIGS. 5a and 5b, an improved mechanism for applying a drive potential to the layer of transparent conductive material 128 is shown. Electrical connection between the power supply and the layer of transparent conductive material 128 is made by connecting the buss bars (or clips 119a) to the area of reflector/electrode 120a, such that the drive potential travels through the area of reflector/electrode 120a and conductive particles 116b in sealing member 116 before reaching the transparent conductor 128. The reflector/electrode must not be present in area 120c, so that there is no chance of current flow from reflector/electrode area 120a to 120b. This configuration is advantageous in that it allows connection to the transparent conductive material 128 nearly all the way around the circumference, and therefore improves the speed of dimming and clearing of the electrochromic media 126.

In such a configuration, sealing member 116 comprises a typical sealing material, e.g., epoxy 116a, with conductive particles 116b contained therein. The conductive particles may be small, such as, for example, gold, silver, copper, etc., coated plastic with a diameter ranging from about 5 microns to about 80 microns, in which case there must be a sufficient number of particles to ensure sufficient conductivity between the reflector/electrode area 120a and the transparent conductive material 128. Alternatively, the conductive particles may be large enough to act as spacers, such as, for example, gold, silver, copper, etc., coated glass or plastic beads. The reflector/electrode 120 is separated into two distinct reflector/electrode areas (120a and 120b, separated by an area 120c devoid of reflector/electrode). There are many methods of removing the reflector/electrode 120 from area 120c, such as, for example, chemical etching, laser ablating, physical removal by scraping, etc. Deposition in area 120c can also be avoided by use of a mask during deposition of reflector/electrode. Sealing member 116 with particles 116b contacts area 120a such that there is a conductive path between reflector/electrode area 120a and the layer of transparent conductive material 128. Thus, electrical connection to the reflector/electrode area 120b that imparts a potential to the electrochromic medium is connected through clips 119b to the electronic circuitry at reflector/electrode area 120d (FIG. 5b). No conductive particles 116b can be placed in this reflector/electrode area 120b because of the possibility of an electrical short between reflector/electrode area 120b and the layer of transparent conductive material 128. If such an electrical short occurred, the electrochromic device would not operate properly. Additionally, no conductive seal 116b should be present in area 120b.

A variety of methods can be used to ensure that no conductive particles 116b enter into this reflector/electrode area 120b, such as, for example, disposing a nonconductive material into the area 120c of reflector/electrode devoid of conductive material. A dual dispenser could be used to deposit the seal 116 with conductive particles 116b onto reflector/electrode area 120a and simultaneously deposit the nonconductive material into reflector/electrode area 120c. Another method would be to cure a nonconductive seal in area 120c and then dispose a conductive material 116c into the edge gap to electrically interconnect reflector/electrode area 120a with transparent conductive layer 128. A general method of ensuring that no conductive particles reach reflector/electrode area 120b is to make sure seal 116 has proper flow characteristics, such that the conductive portion 116b tends to stay behind as the sealant is squeezed out during assembly, and only the non-conductive portion of 116 flows into area 120b. In an alternative embodiment, spacer member 116 need not contain conductive particles and a conductive member or material 116c may be placed on or in the outer edge of member 116 to interconnect transparent conductive material 128 to reflector/electrode area 120a.

Yet another embodiment of an improved electrical interconnection technique is illustrated in FIG. 6, where a first portion of seal member 116 is applied directly onto the third surface 114a and cured prior to the application of reflector/electrode 120. After the reflector/electrode 120 is deposited onto the third surface 114a over the first portion of seal member 116, a portion of the cured seal member 116 is machined off to leave 116i as shown with a predetermined thickness (which will vary depending on the desired cell spacing between the second surface 112b and the third surface 114a). The cell spacing ranges from about 20 microns to about 400 microns, and preferably ranges from about 90 microns to about 230 microns. By curing the first portion of seal member and machining it to a predetermined thickness (116i), the need for glass beads to ensure a constant cell spacing is eliminated. Glass beads are useful to provide cell spacing, however, they provide stress points where they contact reflector/electrode 120 and transparent conductor 128. By removing the glass beads, these stress points are also removed. During the machining, the reflector/electrode 120 that is coated on first portion of seal member 116 is removed to leave an area devoid of reflector/electrode 120. A second portion of seal member 116ii is then deposited onto the machined area of the first portion of seal member 116i or on the coatings on second surface 112b in the area corresponding to 116i, and seal member 116ii is cured after assembly in a conventional manner. Finally, an outer conductive seal member 117 may optionally be deposited on the outer peripheral portion of seal member 116 to make electrical contact between the outer edge of reflector/electrode 120 and the outer peripheral edge of the layer of transparent conductive material 128. This configuration is advantageous in that it allows connection to the transparent conductive material 128 nearly all the way around the circumference, and therefore improves the speed of dimming and clearing of the electrochromic media 126.

Referring again to FIG. 2, rearview mirrors embodying the present invention preferably include a bezel 144, which extends around the entire periphery of each individual assembly 110, 111a, and/or 111b. The bezel 144 conceals and protects the spring clips 134a and 134b of FIG. 3 (or 116a and 116b of FIG. 5a; 116i, 116ii, and 117 of FIG. 6), and the peripheral edge portions of the sealing member and both the front and rear glass elements (112 and 114, respectively). A wide variety of bezel designs are well known in the art, such as, for example, the bezel taught and claimed in above-referenced U.S. Pat. No. 5,448,397. There are also a wide variety of housing well known in the art for attaching the mirror assembly 110 to the inside front windshield of an automobile, or for attaching the mirror assemblies 111a and 111b to the outside of an automobile. A preferred mounting bracket is disclosed in above-referenced U.S. Pat. No. 5,337,948.

The electrical circuit preferably incorporates an ambient light sensor (not shown) and a glare light sensor 160, the glare light sensor being positioned either behind the mirror glass and looking through a section of the mirror with the reflective material completely or partially removed, or the glare light sensor can be positioned outside the reflective surfaces, e.g., in the bezel 144. Additionally, an area or areas of the electrode and reflector, such as 146, may be completely removed or partially removed as described below to permit a vacuum fluorescent display, such as a compass, clock, or other indicia, to show through to the driver of the vehicle. The present invention is also applicable to a mirror which uses only one video chip light sensor to measure both glare and ambient light and which is further capable of determining the direction of glare. An automatic mirror on the inside of a vehicle, constructed according to this invention, can also control one or both outside mirrors as slaves in an automatic mirror system.

The following illustrative examples are not intended to limit the scope of the present invention but to illustrate its application and use:

EXAMPLE 1

Electrochromic mirror devices incorporating a high reflectivity third surface reflector/electrode were prepared by sequentially depositing approximately 700 Å of chromium and approximately 500 Å of silver on the surface of 2.3-millimeter thick sheets of flat soda lime float glass cut to an automotive mirror element shape. A second set of high reflectivity third surface reflector/electrodes were also prepared by sequentially depositing 700 Å of chromium and approximately 500 Å of a silver alloy containing 3 percent by weight palladium on the glass element shapes. The deposition was accomplished by passing the said glass element shapes past separate metal targets in a magnetron sputtering system with a base pressure of 3×10⁻⁶ torr and an argon pressure of 3×10⁻³ torr.

The chromium/silver and chromium/silver 3 percent palladium alloy coated glass automotive mirror shapes were used as the rear planar elements of an electrochromic mirror device. The front element was a sheet of TEC 15 transparent conductor coated glass from LOF cut similar in shape and size to the rear glass element. The front and rear elements were bonded together by an epoxy perimeter seal, with the conductive planar surfaces facing each other and parallel to each other with an offset. The spacing between the electrodes was about 137 microns. The devices were vacuum filled through a fill port left in the perimeter seal with an electrochromic solution made up of:

0.028 molar 5,10-dihydro-5-10-dimethylphenazine

0.034 molar 1,1'-di(3-phenyl(n-propane))-4,4'-bipyridinium di(tetrafluoroborate)

0.030 molar 2-(2'-hydroxy-5'-methylphenyl)-benzotriazole

in a solution of 3 weight percent Elvacite™ 2051 polymethylmethacrylate resin dissolved in propylene carbonate.

The fill port was plugged with an UV cure adhesive, which was cured by exposure to UV light.

The devices were subjected to accelerated durability tests until the seal integrity of the device was breached or the lamination of the reflector/electrode layers or the transparent electrode layers were substantially degraded or dilapidated, at which time the device is said to fail. The first test performed was steam autoclave testing in which the devices were sealed in a water-containing vessel and subjected to 120° C. at a pressure of pounds per square inch (psi). The second test performed was copper-accelerated acetic acid-salt spray (CASS) as described in ASTM B 368-85.

When the electrochromic devices were observed after one day in testing, all of the devices failed to withstand the CASS testing, and all of the devices failed to withstand the steam autoclave testing.

EXAMPLE 2

Other than as specifically mentioned, the devices in this example were constructed in accordance with the conditions and teachings in Example l. Multilayer combination reflector/electrodes were prepared by sequentially depositing approximately 700 Å chromium, approximately 100 Å rhodium, and approximately 500 Å of silver on the surface of the glass element shapes. A second set of multilayer combination reflector/electrodes were also prepared by sequentially depositing approximately 700 Å of chromium, approximately 100 Å rhodium, and approximately 500 Å of a silver alloy containing 3 percent by weight palladium on the surface of said glass element shapes. The electrochromic devices were constructed and tested in accordance with Example 1.

The device incorporating the sequential multilayer combination reflector electrode of chromium, rhodium, and silver withstood steam autoclave testing two times longer and CASS testing 10 times longer than the device in Example 1 before failure occurred. The device incorporating the sequential multilayer combination reflector electrode of chromium, rhodium, and silver 3 percent palladium alloy withstood steam autoclave testing three times longer and CASS testing 10 times longer than devices in Example 1 before failure occurred.

EXAMPLE 3

Other than as specifically mentioned, the devices in this example were constructed in accordance with the conditions and teachings in Example 1. Multilayer combination reflector/electrodes were prepared by sequentially depositing approximately 700 Å chromium, approximately 500 Å molybdenum and approximately 500 Å of a silver alloy containing 3 percent by weight palladium on the surface of said glass element shapes. The electrochromic devices were constructed and tested in accordance with Example 1.

The device incorporating the sequential multilayer combination reflector electrode of chromium, molybdenum, and silver 3 percent palladium alloy withstood CASS testing 10 times longer than devices in Example 1 before failure occurred.

EXAMPLE 4

Other than as specifically mentioned, the devices in this example were constructed in accordance with the conditions and teachings in Example 1. Multilayer combination reflector/electrodes were prepared by sequentially depositing approximately 700 Å chromium, approximately 500 Å of a silver alloy containing 3 percent by weight palladium, and approximately 100 Å of molybdenum on the surface of said glass element shapes. A second set of multilayer combination reflector/electrodes were also prepared by sequentially depositing approximately 700 Å of chromium, approximately 500 Å molybdenum, approximately 500 Å of a silver alloy containing 3 percent by weight palladium, and approximately 100 Å of molybdenum on the surface of said glass element shapes. The electrochromic devices were constructed and tested in accordance with Example 1.

The device incorporating the sequential multilayer combination reflector electrode of chromium, molybdenum, silver 3 percent palladium, and molybdenum withstood steam autoclave testing 25 percent longer and CASS testing twelve times longer than the sequential multilayer combination reflector electrode device of chromium, silver 3 percent palladium, molybdenum before failure occurred. Also, the device incorporating the sequential multilayer combination reflector electrode of chromium, molybdenum, silver 3 percent palladium, molybdenum withstood CASS testing three times longer than the device constructed in Example 3. Finally, the sequential multilayer combination reflector electrode device of chromium, silver 3 percent palladium, molybdenum withstood two times longer in CASS testing and twenty times longer in steam autoclave testing than the sequential multilayer combination reflector electrode device of chromium, silver 3 percent palladium of Example 1.

EXAMPLE 5

Other than as specifically mentioned, the devices in this example were constructed in accordance with the conditions and teachings in Example 1. Multilayer combination reflector/electrodes were prepared by sequentially depositing approximately 700 Å chromium, approximately 100 Å rhodium and approximately 500 Å of silver on the surface of said glass element shapes. A second set of multilayer combination reflector/electrodes were also prepared by sequentially depositing approximately 700 Å of chromium, approximately 100 Å rhodium, and approximately 500 Å of a silver alloy containing 3 percent by weight palladium on the surface of said glass element shapes. A third set of multilayer combination reflector/electrodes was also prepared by sequentially depositing approximately 700 Å of chromium, approximately 100 Å rhodium, and approximately 500 Å of a silver alloy containing 6 percent by weight platinum on the surface of said glass element shapes. A fourth set of multilayer combination reflector/electrodes was also prepared by sequentially depositing approximately 700 Å of chromium, approximately 100 Å rhodium, and approximately 500 Å of a silver alloy containing 6 percent by weight gold on the surface of said glass element shapes. A fifth set of multilayer combination reflector/electrodes was also prepared by sequentially depositing approximately 700 Å of chromium, approximately 100 Å rhodium, and approximately 500 Å of a silver alloy containing 15 percent by weight gold on the surface of said glass element shapes. The electrochromic devices were constructed in accordance with Example 1.

Conductive clips were connected to the offset portions of the front and rear elements of the devices. A power source was connected to the clips and 1.2 volts was applied to the devices continuously for approximately 250 hours at approximately 20° C., with the connection arranged such that the reflector/electrode was the cathode. The device incorporating the sequential multilayer combination reflector electrode of chromium, rhodium, and silver exhibited a yellowing effect within the electrochromic medium. This yellowing phenomenon was not apparent in any of the silver alloy devices.

FIGS. 7A-7G illustrate various alternative constructions for an electrochromic rearview mirror of the present invention, particularly when a light source 170, such as an information display (i.e., compass/temperature display) or signal light, is positioned within the mirror assembly behind the electrochromic mirror. According to the first construction shown in FIG. 7A, the electrochromic rearview mirror was constructed similar to those described above, with the exception that second electrode 120 includes a window 146 in the layer 121 of highly reflective material in a region of second electrode 120 that is in front of light source 170. Electrode 120 further includes a coating 172 of electrically conductive material that is applied cover substantially all of the front surface 114a of rear element 114. Coating 172 is preferably at least partially transmissive so as to enable light emitted from light source 170 to be transmitted through the electrochromic mirror via window 146. By providing electrically conductive coating 172 throughout the entire area of window 146, the electrochromic media 125 in the region of window 146 will respond to the voltage applied to the clips as though window 146 was not even present. Coating 172 may be a single layer of a transparent conductive material. Such a single layer may be made of the same materials as that of first electrode 128 (i.e., tin-doped indium oxide, etc.). Such a single layer preferably has a thickness of between 150 Å and 1600 Å and more preferably between 200 Å and 250 Å, and a sheet resistivity of between about 10 Ω/□ and 150 Ω/□ and preferably less than about 100 Ω/□.

Layer 121 may be made of any of the highly reflective materials described above and is preferably made of silver or a silver alloy. The thickness of reflective layer 121 in the arrangement shown in FIG. 7A is preferably between 30 Å and 800 Å. The thickness of layer 121 will depend on the desired reflectance and transmittance properties. For an inside rearview mirror, layer 121 preferably has a reflectance of at least 60 percent and a transmittance through window 146 of 10 to 50 percent. For an outside mirror, the reflectance is preferably above 35 percent and the transmittance is preferably approximately 10 to 50 percent and more preferably at least 20 percent for those regions that are in front of one of the lights of a signal light (as described in more detail below).

Window 146 in layer 121 may be formed by masking window area 146 during the application of the highly reflective material. At this same time, the peripheral region of the third surface may also be masked so as to prevent materials such as silver or silver alloy (when used as the highly reflective material) from being deposited in areas to which seal 116 must adhere, so as to create a stronger bond between seal 116 and coating 172. Additionally, an area in front of sensor 160 (FIG. 2) may also be masked. Alternatively, an adhesion promoting material can be added to the seal to enhance adhesion between the seal and the silver/silver alloy layer as described in the above-referenced U.S. patent application Ser. No. 09/158,423.

An alternative construction to that shown in FIG. 7A is shown in FIG. 7B, where electrically conductive coating 172 is formed of a plurality of layers 174 and 176. For example, coating 172 may include a first base layer 174 applied directly to front surface 114a of rear element 114, and an intermediate second layer 176 disposed on first layer 174. First layer 174 and second layer 176 are preferably made of materials that have relatively low sheet resistivity and that are at least partially transmissive. The materials forming layers 174 and 176 may also be partially reflective. If the light emitting display behind the partially transmissive window area 146 must be viewed often in bright ambient conditions or direct sunlight, it may be desirable to keep the reflectivity of the window area to a minimum by using metals with low reflectivity or other dark, black or transparent coatings that are electrically conductive.

The material forming layer 174 should exhibit adequate bonding characteristics to glass or other materials of which rear element 114 may be formed, while the material forming layer 176 should exhibit adequate properties so as to bond to the material of layer 174 and provide a good bond between the applied layer 121 and seal 116. Thus, the material used for layer 174 is preferably a material selected from the group consisting essentially of: chromium, chromium-molybdenum-nickel alloys, nickel-iron-chromium alloys, silicon, stainless steel, and titanium. In the most preferred embodiment, layer 174 is made of chromium. The material used to form second layer 176 is preferably a material selected from the group consisting essentially of, but not limited to: molybdenum, rhodium, nickel, tungsten, tantalum, stainless steel, and titanium. In the most preferred embodiment, second layer 176 is formed of nickel, rhodium, or molybdenum. If first layer 174 is formed of chromium, layer 174 preferably has a thickness of between 5 Å and 50 Å. If the layer of chromium is much thicker, it will not exhibit sufficient transmittance to allow light from a light source 170, such as a display or signal light, to be transmitted through window 146. The thickness of layer 176 is selected based upon the material used so as to allow between 10 to 50 percent light transmittance through both of layers 174 and 176. Thus, for a second layer 176 formed of either rhodium, nickel, or molybdenum, layer 176 is preferably between 50 Å and 150 Å. While the thicknesses of layers 174 and 176 are preferably selected to be thin enough to provide adequate transmittance, they must also be thick enough to provide for adequate electrical conductivity so as to sufficiently clear or darken electrochromic media 125 in the region of window 146. The coating 172 should thus have a sheet resistivity of less than 100 Ω/□ and preferably less than 50 Ω/□ to 60 Ω/□.

The arrangement shown in FIG. 7B provides several advantages over the construction shown and described with respect to FIG. 7A. Specifically, the metals used in forming coating 172 contribute to the total reflectance of reflector electrode 120. Accordingly, the layer of the highly reflective material 121 need not be made as thick. If, for example, silver or a silver alloy is used to form layer 121, the layer of thickness is between 50 Å and 150 Å, thereby eliminating some of the material costs in providing the highly reflective layer. Further, the use of reflective metals in forming coating 172 provides for a degree of reflectance within window 146, thereby providing a much more ascetically pleasing appearance than if window 146 were devoid of any reflective material whatsoever. Ideally, coating 172 provides between 30 and 40 percent reflectivity in window 146. If the reflectance in window 146 is too high, bright light will tend to wash out the display in the sense that it eliminates the contrast between the light of the display and light reflecting outward from coating 172.

Another benefit of utilizing metals to form conductive coating 172 is that such metals are much easier and less expensive to process than metal oxides, such as tin-doped indium oxide. Such metal oxides require application in oxygen-rich chambers at very high temperatures, whereas metal layers may be deposited without special oxygen chambers and at much lower temperatures. Thus, the process for applying multiple metal layers consumes much less energy and is much less expensive than the processes for forming metal oxide layers.

A third alternate arrangement for the electrochromic mirror of the present invention is shown in FIG. 7C. The construction shown in FIG. 7C is essentially the same as that shown in FIG. 7B except that a thin silver or silver alloy layer 178 is formed on conductive coating 172 within window 146. By providing only a thin layer 178 of highly reflective material in window 146, adequate transmittance may still be provided through window 146 while increasing the reflectivity and electrical conductivity in that area. Layer 178 may have a thickness of between 40 Å and 150 Å, whereas the layer of highly reflective material 121 in the other areas may have a thickness in the order of between 200 Å and 1000 Å. The thin layer 178 of highly reflective material may be formed by initially masking the area of window 178 while applying a portion of highly reflective layer 121 and then removing the mask during deposition of the remainder of layer 121. Conversely, a thin layer of highly reflective material may first be deposited and then a mask may be applied over window 146 while the remainder of reflective layer 121 is deposited. As will be apparent to those skilled in the art, thin layer 178 may also be formed without masking by depositing highly reflective layer 121 to its full thickness and subsequently removing a portion of layer 121 in the region of window 146.

A modification of the configuration shown in FIG. 7C is illustrated in FIG. 7D. As will be apparent from a comparison of the drawings, the construction of FIG. 7D only differs from that shown in FIG. 7C in that layers 174 and 176 constituting conductive coating 172 are made thinner (designated as thin layers 180 and 181) in the region of reflector/electrode 120 that is in front of light source 170. As such, thin layer 180 may have a thickness of between 5 Å and 50 Å, whereas layer 174 may have thicknesses anywhere between 100 Å and 1000 Å. Similarly, thin layer 181 may be made of the same material as layer 176 but would have a thickness of between 50 Å and 150 Å, while layer 176 may have thicknesses on the order of 100 Å to 1000 Å. Thus, with the construction shown in FIG. 7D, the electrical conductivity, reflectivity, and transmittance within region 146 may be optimized within that region while enabling the reflectance and electrical conductivity in the other regions to be optimized without concern as to the transmittance in those areas.

FIG. 7E shows yet another alternative construction for second electrode 120. In the construction shown in FIG. 7E, second electrode 120 includes an electrically conductive coating 172 and a highly reflective coating 178 formed over the entire third surface 114a of the mirror. By making highly reflective coating 178 uniformly partially transmissive, a light source, such as a display or signal light, may be mounted in any location behind the mirror and is not limited to positioning behind any particular window formed in second electrode 120. Again, for a rearview mirror, second electrode 120 preferably has a reflectance of at least 35 percent for an outside mirror and at least 60 percent for an inside mirror and a transmittance of at least 10 percent. Conductive coating 172 is preferably a single layer of ITO or other transparent conductive materials, but may also consist of one or more layers of the partially reflective/partially transmissive electrically conductive materials discussed above. Highly reflective coating 178 may be constructed using a single, relatively thin, layer of a highly reflective electrically conductive material such as silver, silver alloy, or the other highly reflective materials discussed above. If the highly reflective material is silver or a silver alloy, the thickness of such a thin layer should be limited to about 300 Å or less, and a transparent conductive material, such as ITO or the like, should be utilized as electrically conductive layer 172, such that second electrode 120 may have sufficient transmittance to allow a display or signal light to be viewed from behind the mirror. On the other hand, the thickness of the single layer of highly reflective material should be about 10 Å or more depending upon the material used to ensure sufficient reflectivity.

The inventors have recognized that, when a thin layer of silver or silver alloy is used in a rearview mirror such as those described above, the thin layer imparts a light yellow hue to objects viewed in the reflection. Conversely, transmission through the film is higher for blue light than for red light. One approach to minimizing the yellow hue of the reflected images is to reflect the transmitted blue light back through the mirror. Typically, in the prior art signal or display mirrors a coating of black paint is applied to the fourth surface of the mirror in all areas except for where a display is mounted (if one is employed). Such a black coating was designed to absorb any light that is transmitted through the mirror and its reflective layer(s). To minimize the yellow hue of the reflected image appearing when a thin silver/silver alloy material is used, the black coating may be replaced with a coating 182 that reflects the blue light back through the mirror rather than absorbing such blue light. Preferably, blue paint is used in place of the black paint since the blue backing reflects blue light. Alternatively, coating 182 may be white, gray, or a reflective coating such as chrome, since they too would reflect blue light back through the reflective layer(s) and the remainder of the mirror.

To demonstrate the effectiveness of blue coating 182 on the fourth surface 114b of a mirror, an electrochromic mirror was constructed with a thin layer of silver 178 over a 100 Ω/□ ITO layer 172 as the third surface reflector/electrode 120. The white light reflectivity of the mirror was about 52 percent, and the white light transmission was about 30 percent. The mirror had a noticeably yellow hue in reflection and a blue hue in transmission. The mirror was placed on a black background and the color was measured using a SP-68 Spectrophotometer from X-Rite, Inc. of Grandville, Mich. The measured b* value was +18.72. The same mirror was then placed on a blue background and the color was again measured. With the blue background, the measured b* value fell to +7.55. The mirror thus exhibited noticeably less yellow hue in reflection on the blue background as compared to a black background.

Yet another variation of reflector/electrode 120 is illustrated in FIG. 7F. As illustrated, reflector/electrode 120 is constructed across substantially the entire front surface 114a of rear element 114 with an electrically conductive multi-layer interferential thin-film coating 190. Conductive thin-film coating 190 is preferably tailored to maximize transmittance to light having wavelengths within a narrow band corresponding to the wavelength of light emitted from light source 170. Thus, if light source 170 were a signal light including red, red-orange, or amber AlGaAs or AlInGaP LEDs, the light emitted from such LEDs would have wavelengths in the range of 585 nm to 660 nm, and conductive thin-film coating 190 would be tailored to maximize spectral transmittance at those wavelengths. By increasing the transmittance preferentially within this relatively narrow band of wavelengths, the average luminous reflectance to white light remains relatively high. As will be apparent from the four examples provided below of electrodes constructed using such conductive thin-film coatings, the conductive thin-film coating as so constructed includes a first layer 184 of a first material having a relatively high refractive index, a second layer 186 of a second material formed on first layer 184 where the second material has a relatively low refractive index, and a third layer 187 formed on second layer 186 and made of a material that has a relatively high refractive index. Conductive thin-film coating 190 may also include a thin fourth layer 188 of an electrically conductive material formed on third layer 187. If third layer 187 is not electrically conductive, fourth layer 188 of an electrically conductive material must be disposed on third layer 187. If the first, second, and third layers provide sufficient reflectivity, such a fourth layer 188 may be made of a transparent conductive material. If not, fourth layer 188 may be made of a highly reflective material.

Conductive thin-film coating 190 preferably exhibits: a luminous reflectance of 35 to 95 percent, a reflected C* value of 20 or less, a signal light/display luminous transmittance of 10 percent or more, and a sheet resistance of less than 100 Ω/□. As a measure of comparison, luminous reflection and reflected C* for this coating may be measured using one or more of the CIE illuminants A, B, C, or D55, D65, an equal-energy white source or other broad-band source meeting the SAE definition of white. Luminous reflectance and reflected C* for this coating may be measured at one or more angles of incidence between 10° and 45° from the surface normal. The signal light/display luminous transmittance for this coating may be measured using one or more signal or display sources such as amber, orange, red-orange, red, or deep red LEDs, vacuum fluorescent displays (VFDs), or other lamps or displays, and at one or more angles of incidence between 20° and 55° from the surface normal. As will be apparent to those skilled in the art, "Luminous Reflectance" and "Signal light/display Luminous Transmittance" imply use of either or both of the 1931 CIE 2 degree observer VA or V.sub.λ ' as the eye-weighting functions.

By configuring conductive thin-film coating 190 to have a reflectance, transmittance, electrical conductivity, and a reflected C* value within the above parameters, an electrode may thus be constructed that has medium to high reflectance, substantially neutral reflectance for faithful rendering, medium to high in-band signal light/display transmittance for efficiency and brightness, and low sheet resistance for good electrochromic functionality.

In the specific examples of such a conductive thin-film coating, the first and third materials forming first and third layers 184 and 187, respectively, may be the same or a different material selected from the group consisting essentially of tin-doped indium oxide, titanium dioxide, tin dioxide, tantalum pentoxide, zinc oxide, zirconium oxide, iron oxide, silicon, or any other material having a relatively high reflective index. Second layer 186 may be made of silicon dioxide, niobium oxide, magnesium fluoride, aluminum oxide, or any other material having a low refractive index. First layer 184 may have a thickness of between about 200 Å to 800 Å, second layer 186 may have a thickness of between about 400 Å to 1200 Å, third layer 187 may have a thickness between about 600 Å to 1400 Å, and layer 188 may have a thickness of about 150 Å to 300 Å. Preferably, the electrically conductive material forming fourth layer 188 is made of a highly reflective material such as silver or silver alloy, or of a transparent conductive material such as ITO.

According to a first example of conductive thin-film coating 190, an electrochromic mirror was modeled having a front element 112 having a thickness of 2.2 mm, a first electrode 128 made of ITO and having a thickness of approximately 1400 Å, an electrochromic fluid/gel having a thickness of approximately 137 to 190 microns, and a conductive thin-film coating 190 provided on a rear glass substrate 114. Conductive thin-film coating 190 in this first example included a first layer 184 made of ITO and having a thickness of approximately 750 Å, a second layer 186 made of SiO₂ and having a thickness of approximately 940 Å, a third layer 187 made of ITO and having a thickness of approximately 845 Å, and a fourth layer 188 made of silver and having a thickness of 275 Å. In air, the conductive thin-film coating 190 modeled in this first example exhibited a luminous reflectance of approximately 80.2 percent for white light and a spectral transmittance of approximately 22.5 percent on average for light having wavelengths between 620 nm and 650 nm. Such characteristics make the conductive thin-film coating 190 according to this first example suitable for use either in an inside or outside rearview mirror. When this conductive thin-film coating is applied to the front surface of rear glass element and incorporated into an electrochromic mirror, the overall reflectance decreases and the transmittance increases.

According to a second example, another electrochromic mirror was modeled having the same features as discussed above with the exception that conductive thin-film coating 190 included a first layer 184 made of ITO and having a thickness of approximately 525 Å, a second layer of SiO₂ having a thickness of approximately 890 Å, a third layer 187 made of ITO and having a thickness of approximately 944 Å, and a fourth layer 188 made of silver and having a thickness of approximately 168 Å. In air, the conductive thin-film coating as constructed in the second example has a luminous reflectance of approximately 63 percent for white light incident thereupon at a 20° angle of incidence, and a spectral transmittance of approximately 41 percent on average for light having wavelengths in the 620 nm to 650 nm wavelength range at 20° angle of incidence. Such a conductive thin-film coating 190 is particularly suitable for an outside rearview mirror. When this conductive thin-film coating is applied to the front surface of rear glass element and incorporated into an electrochromic mirror, the overall reflectance decreases and the transmittance increases.

A conductive thin-film coating according to a third example was modeled that was made of the same materials as described for the first two conductive thin-film coatings except that first layer 184 had a thickness of approximately 525 Å, second layer 186 had a thickness of approximately 890 Å, third layer 187 had a thickness of approximately 945 Å, and fourth layer 188 had a thickness of approximately 170 Å. In air, the conductive thin-film coating thus modeled had a luminous reflectance of 63 percent at 20° angle of incidence for illumination with white light, and an average spectral transmittance of approximately 41 percent for light having wavelengths between the 620 nm and 650 nm wavelength range at 20° angle of incidence. When this conductive thin-film coating is applied to the front surface of rear glass element and incorporated into an electrochromic mirror, the overall reflectance decreases and the transmittance increases.

According to a fourth example, a non-conductive three layer interference coating available from Libbey Owens Ford (LOF) of Toledo, Ohio, is used in combination with a conductive fourth layer 188 of ITO or the like. The thin film stack available from LOF has a first layer 184 of Si, a second layer 186 of SiO₂, and a third layer 187 of SnO₂. This coating has a reflectance of approximately 80 percent and a transmittance of approximately 4 percent for white light, and transmittance of 7 to 10 percent for light having wavelengths in the 650 to 700 nm range. The transmittance in the 650 to 700 nm range makes this thin film stack particularly suitable for a signal mirror that utilizes a red light source. While the SnO₂, SiO₂ and Si used in the LOF thin film stack are not highly reflective materials by themselves (particularly when applied as a thin layer), the alternating layers of such materials having high and low refractive indices produce the requisite high level of reflectivity. The poor electrical conductivity of this thin film stack requires that it be implemented with an electrically conductive layer that has good electrical conductivity, such as a layer of ITO or the like. The LOF thin film stack overcoated with an ITO layer having a half-wave thickness exhibited a sheet resistance of 12 Ω/□. When the ITO/LOF thin-film stack was used as a second electrode for an electrochromic mirror, the mirror had a reflectance of 65 percent. Several different displays were placed behind the assembled mirror and were all easily observed.

FIG. 7G shows yet another alternate construction that is very similar to that shown in FIG. 7F, with the exception that only three layers are utilized for the electrically conductive multi-layer thin-film coating 190. According to the construction shown in FIG. 7G, thin-film coating 190 includes a first layer 184 made of a material having a high refractive index such as the materials noted above in connection with FIG. 7F, a second layer made of a material having a low refractive index such as those materials also discussed above for layer 186 in FIG. 7F, and a third layer 188 of electrically conductive material. Layer 188 need not be made of a material having a high refractive index, but rather may be made of any electrically conductive material suitable for use in an electrochromic mirror. For example, layer 188 may be a highly reflective metal, such as silver or a silver alloy, or may be a metal oxide, such as ITO. To illustrate the feasibility of such a coating, two examples are described below.

In a first example, an electrochromic mirror was modeled having a first layer 184 of ITO deposited on a front surface of rear glass substrate 114 at a thickness of 590 Å, a second layer 186 of silicon dioxide applied at a thickness of 324 Å over first layer 184, and a third layer 188 of silver having a thickness of 160 Å applied over second layer 186. The electrochromic mirror was then illuminated with a CIE illuminant D65 white light source at an angle of incidence of 20°. When illuminated with such white light, the mirror exhibited a luminance reflectance of 52 percent and a* and b* values of approximately 1.0 and 5.0, respectively. When illuminated with a red LED source at 35° angle of incidence, the mirror exhibited a luminous transmittance of 40 percent.

According to a second example of the structure shown in FIG. 7G, an electrochromic mirror was modeled having a first layer 184 of silicon deposited at a thickness of 184 Å on the front surface of glass substrate 114, a second layer 186 deposited on first layer 184 and formed of silicon dioxide at a thickness of 1147 Å, and a third layer 188 of ITO of a thickness of 1076 Å applied over second layer 186. The electrochromic mirror having such a coating was illuminated with a CIE illuminant D65 white light source at 20° angle of incidence. When illuminated with such white light, the mirror exhibited a luminous reflectance of 54 percent and a* and b* values of -2.5 and 3.0, respectively. When illuminated with a red LED source at 35° angle of incidence, the mirror exhibited a luminous transmittance of approximately 40 percent.

Considering that the above two three-layer examples exhibited luminous reflectance in excess of 50 percent and transmittance of approximately 40 percent, a mirror constructed as shown in FIG. 7G meets the specific objectives noted above with respect to FIG. 7F, and is therefore suitable for use in an outside electrochromic rearview mirror incorporating a signal light.

As will be apparent to those skilled in the art, the electrically conductive multi-layer thin-film coating described above may be implemented as a third surface reflector for an electrochromic mirror regardless of whether the electrochromic medium is a solution-phase, gel-phase, or hybrid (solid state/solution or solid state/gel).

Although the above alternative constructions shown and described with respect to FIGS. 7A-7G do not include a flash-over protective layer such as layer 124 shown in FIG. 3, those skilled in the art will understand that such a flash-over layer may be applied over any of the various reflector/electrode 120 constructions shown in FIGS. 7A-7G.

FIG. 8 shows an outside rearview mirror assembly 200 constructed in accordance with another embodiment of the present invention. Outside rearview mirror assembly 200 includes a mirror 210, which is preferably an electrochromic mirror, an external mirror housing 212 having a mounting portion 214 for mounting mirror assembly 200 to the exterior of a vehicle, and a signal light 220 mounted behind mirror 210. To enable the light from signal light 220 to project through electrochromic mirror 210, a plurality of signal light areas 222 are formed in the electrode/reflector of mirror 210 that include window regions containing electrically conductive material that is at least partially transmissive similar to the information display and glare sensor window areas described above with respect to the other embodiments of the present invention. Electrochromic mirror 210 may further include a sensor area 224 disposed within the reflective coating on electrochromic mirror 210 and similarly include window regions containing electrically conductive material that is at least partially transmissive so as to allow some of the incident light to reach a sensor mounted behind sensor area 224. Alternatively, sensor 224 could be used to sense glare in night driving conditions and control the dimming of the exterior mirror independently or verify that the mirrors are being sufficiently dimmed by the control circuit in the interior mirror. In such a case, a more sensitive photo sensor may be required, such as a CdS sensor.

Signal light 220 is preferably provided to serve as a turn signal light and is thus selectively actuated in response to a control signal generated by a turn signal actuator 226. The control signal is therefore applied to signal light 220 as an intermittent voltage so as to energize signal light 220 when a driver has actuated the turn signal lever. As shown in FIG. 11, when vehicle B is in the blind spot of vehicle A where the driver of vehicle A cannot see vehicle B, the driver of vehicle B cannot see the turn signal on the rear of vehicle A. Thus, if the driver of vehicle A activates the turn signal and attempts to change lanes while vehicle B is in a blind spot, the driver of vehicle B may not receive any advance notice of the impending lane change, and hence, may not be able to avoid an accident. By providing a turn signal light in an outside rearview mirror assembly 200 of vehicle A, the driver of an approaching vehicle B will be able to see that the driver of vehicle A is about to change lanes and may thus take appropriate action more quickly so as to avoid an accident. As illustrated in FIG. 11 and described in more detail below, the signal light is preferably mounted within mirror assembly at an angle to the mirror surface to project the light from the signal light outward into the adjacent lanes in the blind spot areas proximate the vehicle.

Referring again to FIG. 8, electrochromic mirror 220 may be controlled in a conventional manner by a mirror control circuit 230 provided in the inside rearview mirror assembly. Inside mirror control circuit 230 receives signals from an ambient light sensor 232, which is typically mounted in a forward facing position on the interior rearview mirror housing. Control circuit 230 also receives a signal from a glare sensor 234 mounted in a rearward facing position of the interior rearview mirror assembly. Inside mirror control circuit 230 applies a control voltage on a pair of lines 236 in a conventional manner, such that a variable voltage is applied essentially across the entire surface of electrochromic mirror 210. Thus, by varying the voltage applied to lines 236, control circuit 230 may vary the transmittance of the electrochromic medium in mirror 210 in response to the light levels sensed by ambient sensor 232 and glare sensor 234. As will be explained further below, an optional third control line 238 may be connected between the inside mirror control circuit 230 and a variable attenuator 260 provided in outside mirror assembly 200, so as to selectively attenuate the energizing signal applied on lines 228 from turn signal actuator 226 to the signal light 220 in response to the control signal sent on line 238. In this manner, inside mirror control circuit 230 may selectively and remotely control the intensity of signal light 220 based upon information obtained from sensors 232 and 234 and thereby eliminate the need for a sensor to be mounted in each mirror assembly as well as the associated sensor area 224.

Mirror assembly 200 may further include an electric heater (not shown) provided behind mirror 210 that is selectively actuated by a heater control circuit 240 via lines 242. Such heaters are known in the art to be effective for deicing and defogging such external rearview mirrors. Mirror assembly 200 may optionally include a mirror position servomotor (not shown) that is driven by a mirror position controller 244 via lines 246. Such mirror position servomotors and controls are also known in the art. As will be appreciated by those skilled in the art, mirror assembly 200 may include additional features and elements as are now known in the art or may become known in the future without departing from the spirit and scope of the present invention.

An exemplary signal light subassembly 220 is shown in FIG. 9. Such a signal light 220 is disclosed in U.S. Pat. Nos. 5,361,190 and 5,788,357, which disclose the signal light in combination with dichroic exterior rearview mirrors that are not electrochromic. The disclosures of the signal light assembly in U.S. Pat. Nos. 5,361,190 and 5,788,357 is incorporated herein by reference. As explained below, however, the same signal light subassembly may be used in connection with an electrochromic mirror as may modified versions of the signal light subassembly shown in FIG. 9.

As shown in FIG. 9, signal light 220 includes a printed circuit board 250 that, in turn, is mounted within a housing 252 having a peripheral edge that serves as a shroud (see FIGS. 6A and 6B) to block any stray light from exiting the signal light assembly. Signal light 220 preferably includes a plurality of LEDs 254 that are mounted to circuit board 250. LEDs 254 may be mounted in any pattern, but are preferably mounted in a pattern likely to suggest to other vehicle operators that the vehicle having such signal mirrors is about to turn. LEDs 254 may be LEDs that emit red or amber light or any other color light as may prove desirable. LEDs 254 are also preferably mounted to circuit board 250 at an angle away from the direction of the driver. By angling LEDs relative to mirror 210, the light projected from LEDs 254 may be projected outward away from the driver towards the area C in which the driver of another vehicle would be more likely to notice the signal light, as shown in FIG. 11. Hence, the potential glare from the signal light as viewed by the driver may be effectively reduced.

Signal light 220 may optionally include a day/night sensor 256 also mounted to circuit board 250. If sensor 256 is mounted on circuit board 250, a shroud 257 is also preferably mounted to shield sensor 256 from the light generated by LEDs 254. Also, if sensor 256 is provided in signal light 220, a day/night sensing circuit 258 may also be mounted on circuit board 250 so as to vary the intensity of LEDs 254 in response to the detection of the presence or absence of daylight by sensor 256. Thus, if sensor 256 detects daylight, circuit 258 increases the intensity of the light emitted from LEDs 254 to their highest level and decreases the intensity of the emitted light when sensor 256 detects that it is nighttime. The above-noted signal light disclosed in U.S. Pat. Nos. 5,361,190 and 5,788,357 includes such a day/night sensor 256 and associated control circuit 258, and therefore, further description of the operation of the signal light in this regard will not be provided.

As an alternative to providing a day/night sensor 256 in each of the vehicle's exterior rearview mirrors, a variable attenuator 260 or other similar circuit may be provided to vary the driving voltage applied from the turn signal actuator 226 on line 228 in response to a control signal delivered from inside mirror control circuit 230 on a dedicated line 238. In this manner, inside mirror control circuit 230 may utilize the information provided from ambient light sensor 232 as well as the information from glare sensor 234 to control the intensity of the light emitted from LEDs 254 and signal light 220. Since the ambient light and glare sensors 232 and 234 are already provided in an internal electrochromic rearview mirror, providing for such remote control by the inside mirror control circuit 230 eliminates the need for providing additional expensive sensors 256 in the signal light 220 of each exterior mirror assembly. As an alternative to running a separate wire 258 to each of the outside rearview mirrors, variable attenuator 260 may be provided in the dashboard proximate the turn signal actuator or otherwise built into the turn signal actuator, such that a single control line 238' may be wired from inside mirror control circuit 230 to the turn signal actuator as shown in FIG. 8.

The intensity of the light emitted from the LEDs may thus be varied as a function of the light level sensed by ambient sensor 232 or glare sensor 234, or as a function of the light levels sensed by both sensors 232 and 234. Preferably, LEDs 254 are controlled to be at their greatest intensity when ambient sensor 232 detects daylight and at a lesser intensity when sensor 232 detects no daylight. Because the transmittance of the electrochromic medium is decreased when excessive glare is detected using glare detector 234, the intensity of LEDs 254 is preferably correspondingly increased so as to maintain a relatively constant intensity at nighttime.

Electrochromic mirror 210 may be constructed in accordance with any of the alternative arrangements disclosed in FIGS. 7A-7F above, where light source 170 represents one of LEDs 254 of signal light subassembly 220. Accordingly, each possible combination of the various constructions shown in FIGS. 7A-7F with signal light subassembly 220 are not illustrated or described in further detail. As but one example, however, FIG. 10 shows the manner in which a signal light subassembly 220 could be mounted behind a preferred construction that is otherwise identical to that shown in FIG. 7C. As apparent from a comparison of FIG. 7C and FIG. 10, each of signal light areas 222 corresponds to window 146 of FIG. 7C. As discussed above, for an outside rearview mirror the reflectance of reflector/electrode 120 is preferably at least 35 percent and the transmittance is preferably at least 20 percent so as to meet the minimum reflectance requirements and yet allow sufficient transmittance so that the light emitted from signal light 220 may be readily noticed by the driver of an approaching vehicle.

Although the present invention has been described as providing a signal light that is used as a turn signal, it will be appreciated by those skilled in the art that the signal light could function as any other form of indicator or signal light. For example, the signal light could indicate that a door is ajar so as to warn drivers of approaching vehicles that a vehicle occupant may be about to open a door into oncoming traffic, or the light behind the mirror may be an indicator light to indicate that the mirror heaters have been turned on.

While the signal light of the present invention has been described above as preferably being made of a plurality of LEDs, the signal light may nevertheless be made of one or more incandescent lamps, or any other light source, and an appropriately colored filter without departing from the spirit or scope of the present invention.

While the invention has been described in detail herein in accordance with certain preferred embodiments thereof, many modifications and changes therein may be effected by those skilled in the art without departing from the spirit of the invention. Accordingly, it is our intent to be limited only by the scope of the appending claims and not by way of the details and instrumentalities describing the embodiments shown herein. 

The invention claimed is:
 1. A partially reflective, partially transmissive electrode for an electrochromic rearview mirror having first and second transparent substrates each having front and rear surfaces, said electrode comprising:a first layer of a first material having a relatively high refractive index; a second layer of a second material having a relatively low refractive index disposed on said first layer; and a third layer of a third material disposed on said second layer, said third material having a relatively high refractive index, wherein said first, second, and third layers together exhibit partial reflectance and partial transmittance.
 2. The electrode as defined in claim 1, wherein said third material is the same as said first material.
 3. The electrode as defined in claim 2, wherein said first and third materials are selected from the group consisting essentially of tin-doped indium oxide, titanium dioxide, tin dioxide, tantalum pentoxide, zinc oxide, zirconium oxide, iron oxide, and silicon.
 4. The electrode as defined in claim 1, wherein said first, second, and third materials are electrically conductive.
 5. The electrode as defined in claim 1 and further including a fourth layer of an electrically conductive material disposed on said third layer.
 6. The electrode as defined in claim 5, wherein said fourth layer is made of an electrically conductive, highly reflective material.
 7. The electrode as defined in claim 6, wherein said highly reflective material is silver or silver alloy.
 8. The electrode as defined in claim 7, wherein said layer of highly reflective material has a thickness of about 150 Å to 300 Å.
 9. The electrode as defined in claim 5, wherein said fourth layer is made of an electrically conductive transparent material.
 10. The electrode as defined in claim 9, wherein said electrically conductive transparent material is tin-doped indium oxide.
 11. The electrode as defined in claim 1, wherein said first material is selected from the group consisting essentially of tin-doped indium oxide, titanium dioxide, tin dioxide, tantalum pentoxide, zinc oxide, zirconium oxide, iron oxide, and silicon.
 12. The electrode as defined in claim 11, wherein said first layer has a thickness of about 200 Å to 800 Å.
 13. The electrode as defined in claim 1, wherein said second material is selected from the group consisting essentially of silicon dioxide, niobium oxide, magnesium fluoride, and aluminum oxide.
 14. The electrode as defined in claim 13, wherein said second layer has a thickness of about 400 Å to 1200 Å.
 15. The electrode as defined in claim 1, wherein said third material is selected from the group consisting of tin-doped indium oxide, titanium dioxide, tin dioxide, tantalum pentoxide, doped zinc oxide, zirconium oxide, iron oxide, and silicon.
 16. The electrode as defined in claim 15, wherein said third layer has a thickness of about 600 Å to 1400 Å.
 17. The electrode as defined in claim 1, wherein said electrode has an average luminous reflectance of at least about 60 percent over all visible wavelengths and an average transmittance of at least 10 percent in 585 to 650 nm wavelength range.
 18. The electrode as defined in claim 1, wherein said electrode has an average luminous reflectance of at least about 35 percent over all visible wavelengths and an average transmittance of at least about 10 percent in 585 to 650 nm wavelength range.
 19. The electrode as defined in claim 1, wherein said electrode has a sheet resistance of less than about 100 Ω/□.
 20. The electrode as defined in claim 1 and further including a fourth layer of a silver/silver alloy disposed on said third layer, wherein said first material is tin-doped indium oxide, said second material is silicon dioxide, and said third material is tin-doped indium oxide.
 21. The electrode as defined in claim 1, wherein said electrode has an average luminous reflectance of at least about 35 percent over all visible wavelengths.
 22. A partially reflective, partially transmissive electrode for an electrochromic rearview mirror having a first and second transparent substrates each having front and rear surfaces, said electrode comprising:a first layer of a first material having a relatively high refractive index; a second layer of a second material having a relatively low refractive index disposed on said first layer; and a third layer of an electrically conductive third material disposed on said second layer, wherein said first, second, and third layers together exhibit partial reflectance and partial transmittance.
 23. The electrode as defined in claim 22, wherein said electrically conductive third material is a highly reflective material.
 24. The electrode as defined in claim 23, wherein said highly reflective material is silver or silver alloy.
 25. The electrode as defined in claim 24, wherein said layer of highly reflective material has a thickness of about 160 Å.
 26. The electrode as defined in claim 24, wherein said silver alloy is a combination of silver and an element selected from the group consisting essentially of gold, platinum, rhodium, and palladium.
 27. The electrode as defined in claim 22, wherein said electrically conductive third material is substantially transparent.
 28. The electrode as defined in claim 27, wherein said transparent conductive material is tin-doped indium oxide.
 29. The electrode as defined in claim 22, wherein said first material is selected from the group consisting essentially of tin-doped indium oxide, titanium dioxide, tin dioxide, tantalum pentoxide, zinc oxide, zirconium oxide, iron oxide, and silicon.
 30. The electrode as defined in claim 22, wherein said second material is selected from the group consisting essentially of silicon dioxide, niobium oxide, magnesium fluoride, and aluminum oxide.
 31. The electrode as defined in claim 22, wherein said third material is selected from the group consisting essentially of tin-doped indium oxide, titanium dioxide, tin dioxide, tantalum pentoxide, doped zinc oxide, zirconium oxide, iron oxide, and silicon.
 32. The electrode as defined in claim 22, wherein said electrode has an average luminous reflectance of at least about 50 percent over all visible wavelengths and an average transmittance of at least about 40 percent in 585 to 650 nm wavelength range.
 33. The electrode as defined in claim 22, wherein said electrode has a sheet resistance of less than about 100 Ω/□.
 34. The electrode as defined in claim 22, wherein said first layer is made of tin-doped indium oxide, said second layer is made of silicon dioxide, and said third layer is made of silver/silver alloy.
 35. The electrode as defined in claim 22, wherein said first layer is made of silicon, said second layer is made of silicon dioxide, and said third layer is made of tin-doped indium oxide.
 36. The electrode as defined in claim 22, wherein said electrode has an average luminous reflectance of at least about 35 percent over all visible wavelengths.
 37. An external rearview mirror assembly comprising: a housing; an electrochromic mirror mounted in said housing, said electrochromic mirror including the electrode of claim 22; and a signal light mounted in said housing behind said electrochromic mirror. 